Japan’s Giant Crayfish

Posted by: Loren Coleman on March 8th, 2009

Continuing a yearly tradition since he began guest blogging here, Brent Swancer passes along his third March 8th posting. – Loren.

Japan’s Giant Crayfish

By Brent Swancer

Is there an unidentified giant crayfish inhabiting Japan’s lakes? For years, occasional reports of extremely large, unexplained crayfish have surfaced in northern Japan, most notably in Hokkaido’s Lake Mashu.

Known to the Ainu people as “Kamuy-tou,” or “The Lake of the Gods,” Lake Mashu is located in the northeast part of Hokkaido, Japan. It is a caldera lake, formed in the crater of a dormant volcano approximately 11,000 years ago.

Surrounded by high, sheer cliffs, Lake Mashu lies 315 meters (1,033 ft) above sea level, is 20 km in circumference, and 212 meters (695 ft) deep at its deepest point. The lake is notable for having some of the clearest water in the world. Lake Mashu is also famous for the thick fog that veils it for most of the summer months, resulting in it’s nickname “foggy Lake Mashu.” The lake is quite remote, with access to the shoreline limited.

Since at least the 1970s, there have been reports of something strange in the lake. Accounts have surfaced over the years of crayfish far exceeding the size of any known to be in Japan. In 1978 and 1985, trout poachers are reported to have captured extremely large crayfish in the lake. In total, there were three alleged specimens gathered by these poachers, although the claims could not be confirmed due to the illegal nature of the circumstances surrounding the capture of the creatures. Another account comes from one author of a survey of known crayfish in the lake, entitled “Crayfish in Lake Mashu, Hokkaido,” who reported that he had once captured a male crayfish specimen when he was a young man which had a carapace that measured a whopping 47 cm (18.5 inches) in length. It is important to remember that this figure is only for the length of the carapace, and not the total length of the specimen, which would be much longer.

There have been other scattered reports of giant crayfish in the lake as well. In one such report, a fisherman described seeing a crayfish crawling along the bottom in the clear water of the lake that he estimated as being at least 3 feet long.

Japan has only one species of endemic crayfish, the Japanese crayfish (Cambaroides japonicus), that inhabits the cold, clean waters of lakes, ponds, and streams in northern Japan. It is not a particularly large crayfish, reaching sizes of only 4 to 7 cm (2 to 3 inches) in total length, with an average carapace length of 3.5 cm (1.4 inches). Perhaps more importantly, it is not known to inhabit Lake Mashu.

The other two species of crayfish known to live in the wild in Japan are introduced species. One is the the invasive Louisiana crayfish, or red swamp crayfish (Procambarus clarkii) from North America. It is found all over Japan, on all of the major islands. This species is even smaller than the signal crayfish, reaching sizes of 5.5 to 12 cm (2.2 to 4.7 inches) in total length. It too is not known to be present in Lake Mashu.

The only species of crayfish known to inhabit Lake Mashu is the introduced signal crayfish of North America (Pacifastacus leniusculus). This species was imported to Lake Mashu from Oregon and the Columbia River system in the 1930s as a potential food source. The signal crayfish reaches sizes of up to 15cm (5.9 inches) in length, with an average carapace length of 3 to 6 cm (1.2 to 2.4 inches), far from the enormous sizes reported for the mystery crayfish of Lake Mashu.

In the summer of 1992, there was a study of crayfish in the lake. Of the 171 males and 517 females caught in tangle nets during this study, no specimen had a carapace length of more than 5.7 cm (2.2 inches). Incidentally, this species has since been introduced to other lakes throughout Hokkaido, where it is notable for posing a serious threat to native Japanese crayfish. The signal crayfish has seriously threatened the native species in many areas through predation, competition, and as a carrier of crayfish plague, a type of water mould that infects crayfish. It is so invasive that it was put on the list of alien species that are banned in Japan under the Invasive Alien Species Law enacted in February, 2006.

So what could be behind the reports of mysterious giant crayfish? The fish in Lake Mashu, such as sockeye salmon and rainbow trout, as well as the sole species of crayfish known to be there, are all introduced from elsewhere. Since Lake Mashu is a Caldera lake, there are no endemic species there. There are also no rivers or significant waterways connected to the lake. The lake is a completely isolated habitat.

Perhaps when trying to ascertain what is going on, the first possibility to consider is other types of introduced, exotic crayfish. The world’s largest species of crayfish, indeed the largest freshwater invertebrate, is the Tasmanian giant freshwater crayfish (Astacopsis gouldi), above and below.

These crayfish reach average sizes of at least 40 cm (15.7 inches) in total length, but even huger sizes of up to 80 cm (31.5 inches) in total length and weighing up to 6 kg (13.2 lbs) have been recorded. The second largest is the Murray crayfish (Euastacus armatus) of the Australian mainland, which reaches overall lengths of 20 to 30 cm (7.9 to 11.8 inches) and weights of up to 2 kg (4.4 lbs). These vulnerable species are both currently protected by Australian law, and they are also banned in Japan by the 2006 Invasive Species Law.

Crayfish are popular as pets in Japan, so it seems at least plausible that perhaps some unsuspecting aquarists have bought specimens of one of these Australian species and dumped them when they got much bigger than expected. However, although these Australian species are large, the sizes still don’t seem to add up. Keep in mind that the measured Lake Mashu specimen I mentioned earlier was recorded as being 18.5 inches long for its carapace alone (not it’s total length). The total length of such a monster from head to tail would be bigger than even the largest known crayfish species.

One possibility is that the known crayfish in the lake have seen some instances of gigantism. Beyond insular gigantism (island gigantism) in their isolated lake environment, there are several factors that could contribute to large sizes in the crayfish. For instance, these large sizes could come about as an adaptation for competing for scarcer food resources, which could possibly lead to delayed sexual maturity that would result in greater size. The Lake Mashu specimen that was measured was a male that was described as having exceptionally large chelae, or pincers. Since adult male signal crayfish in the lake do not exhibit secondary sexual characteristics in their chelae, this suggests that some degree of neoteny (delayed maturity) could be occurring. This means the specimen could even have possibly been still growing.

Gigantism in the crayfish could also have occurred as an adaptation for more efficient temperature regulation and lesser need for continuous activity in the cold depths of the lake. Although crayfish favor cold water, Lake Mashu reaches extremely low temperatures, and is frozen over from December to April. Organisms with lower surface to mass ratios can manage body heat better, and minimize heat lost to their surroundings, a phenomenon known as gigantothermy. This characteristic can be seen in some deep sea and cold water arthropods, so perhaps something similar is happening in Lake Mashu with crayfish.

The high oxygen content of the lake may also be a contributing factor. One suggested hypothesis for phenomena such as Polar gigantism (the tendency for some cold dwelling, polar animals to reach larger sizes), is that high availability of oxygen relieves constraints on the body’s ability to transport oxygen which in turn allows for attaining larger sizes. Lake Mashu is an oligotrophic lake, meaning it has generally low nutrient levels and productivity. For instance, there is a distinct lack of algea in oligotrophic lakes, a condition which actually contributes to the clear water seen in places like Lake Mashu. The flip side is that this cold, clear water provides high oxygen levels, making it an ideal habitat for animals like the lake’s introduced rainbow trout and salmon, which favor such conditions. This high oxygen level could have perhaps contributed to gigantism in the crayfish.

Larger size has also shown in studies to be a distinct advantage for both inter- and intra- specific competition for shelter among crayfish. Shelter is an important, limited resource for crayfish, perhaps especially so in a place like Lake Mashu, which has a bottom that is almost flat and covered with pumice deposits. Maybe some specimens have begun to get larger due to ever increasing competition for prime hiding places.

The only problem with hypotheses on factors for gigantism is the time frame involved. Changes like this typically take a long time, and crayfish have only been present in the lake since the 1930s. Crayfish are generally fairly long lived creatures, that take many years to reach sexual maturity. This means there simply will not have been many generations born in the lake during which such changes would occur. The chances of such dramatic size adaptations developing so rapidly, and in so few generations, seem somewhat low.

Whatever they are, the giant crayfish of Lake Mashu make for an interesting mystery.

Clawnote: Of course, being from Maine, darn, these just look like our run-of-the-mill lobsters (but, of course, those are marine, not freshwater animals)! ~ Thanks, Loren.


In June 2006, 16-year-old Louie Smith caught this giant lobster while fishing off a pier in Kent, UK. The lobster weighed 11 lbs 3 oz and could have been 100 years old. After posing for a photograph the lobster was thrown back into the ocean.

In January 2009, Neil Robinson, of Portsmouth N.H., carries an allegedly 140 year old, 20-pound lobster to freedom in Kennebunkport, Maine.

Finally, an unidentified chef holds aloft two giant crayfishes for diners in
South Africa.

Loren Coleman About Loren Coleman
Loren Coleman is one of the world’s leading cryptozoologists, some say “the” leading living cryptozoologist. Certainly, he is acknowledged as the current living American researcher and writer who has most popularized cryptozoology in the late 20th and early 21st centuries. Starting his fieldwork and investigations in 1960, after traveling and trekking extensively in pursuit of cryptozoological mysteries, Coleman began writing to share his experiences in 1969. An honorary member of Ivan T. Sanderson’s Society for the Investigation of the Unexplained in the 1970s, Coleman has been bestowed with similar honorary memberships of the North Idaho College Cryptozoology Club in 1983, and in subsequent years, that of the British Columbia Scientific Cryptozoology Club, CryptoSafari International, and other international organizations. He was also a Life Member and Benefactor of the International Society of Cryptozoology (now-defunct). Loren Coleman’s daily blog, as a member of the Cryptomundo Team, served as an ongoing avenue of communication for the ever-growing body of cryptozoo news from 2005 through 2013. He returned as an infrequent contributor beginning Halloween week of 2015. Coleman is the founder in 2003, and current director of the International Cryptozoology Museum in Portland, Maine.

49 Responses to “Japan’s Giant Crayfish”

  1. Kitsos responds:

    Mmmmmm…..jumbo gumbo!
    Lets send MQ over and see if they can get their toes pinched.

  2. kittenz responds:

    We have crayfish, (we call ’em crawdads) most of which never grow to more than about 6 to 8 inches in length, in the creeks and rivers here in Kentucky. There are also crayfish that are more terrestrial in nature, inhabiting holes they dig in the creekbanks, which tend to grow a bit larger (and pack a mean pinch if you get too close).

    One of my fondest memories of childhood is wading the creeks “catching crawdads”. We would catch the little crawdads, keep them in a bucket for a day or maybe overnight, then turn them loose again.

  3. MrInspector responds:

    One word, “jambalaya!”

  4. MountDesertIslander responds:

    I believe lobsters continue to grow throughout their lives. Stories abound in Maine of 4 foot long lobsters living close to shore in remote tidal estuaries where food is plentiful. Would crayfish not keep growing if left alone in the wild?

    In the backwoods of Pennsylvania the locals checked the safety of their spring water by placing crayfish in their catch basins. If the crayfish lived, the farmers believed that the water was safe for humans. I remember a farmer showing me truely spectacular sized crayfish that had lived in his spring water collection basin for years. This guy was almost 9 inches in total length. Up until that time the largest crayfish I had seen in the wild was around 4 inches in length, that was pretty awe inspiring.

    Am I wrong in guessing that considering the enormity of the lake and lack of size restrictions due the habitat it would seem possible a species of crayfish could grow to such sizes?

  5. coelacanth1938 responds:

    Giant lobsters did indeed exist. The early settlers used to catch them and feed them to their hogs *sighs*.

  6. red_pill_junkie responds:

    Great article, mystery_man! ^_^

  7. Richard888 responds:

    In a lake that is a completely isolated habitat and has no discovered endemic species, is it natural for the only undiscovered species to grow to a huge size? Something doesn’t feel right about this. And since Japan has a history of crayfish importation and given the proximity of Australia, the Tasmanian giant freshwater crayfish theory shouldn’t be dismissed that easily.

  8. Dj Plasmic Nebula responds:

    i want to see a gigantic Crayfish and Lobster and Crab.. They are beautiful creatures.

    Maybe some sea men saw gigantic Crayfish, lobster or crabs and called it a sea beast…. knowing how most animals don’t always surface the water to the point you only see part of their body…

  9. DG responds:

    Speaking of giant lobsters…

    “Caught off eastern Canada in 1977, the biggest lobster ever recorded weighed in at 44 pounds (20 kilograms) and stretched to 41 inches (106 centimeters).”

    I’ve also read that seafood processing plants around the Caribbean, fairly frequently acquire giant lobsters in the 20 to 40 lb range, which they have a hard time selling. (I’ve read that they practically give them away for free.) Their equipment is not suited to processing lobsters of this size, and the average household doesn’t have a pot big enough to cook it (or the courage to try, I would imagine.) I wouldn’t be surprised of some larger than 44 pounds (the record) have been caught, but simply weren’t submitted for the record books.

  10. mystery_man responds:

    Richard888- There would be no natural undiscovered species in the lake. It was formed in the crater of a volcano only 11,000 years ago. ALL of the species of fish and crustaceans there are introduced. I certainly don’t think the Tasmanian freshwater crayfish should be dismissed, but the ones reported from this lake are far larger than any ever found of that species.

    Some people here are mentioning lobster, which are similar and do get much larger than crayfish, but they are a saltwater, marine animal. This lake is not only freshwater, it is in no way connected to the ocean.

    If you look at freshwater crayfish species, none of them get as large as what has been reported in this lake.

    MountDesertIslander- What you suggest is exactly what I was getting at in the article. There could be some sort of factors leading to gigantism, but it is a huge jump compared to sizes reported for other freshwater crayfish. Something is definitely going on in that lake, I’m just not sure what. There are predatory fish in the lake, so it’s not as if young crayfish would have a blank check to keep growing and growing. But certainly some size constraint has been removed here.

  11. CryptidHuntr responds:

    the mystery cray fish could be overgrown versiones of the one already in there

  12. dogu4 responds:

    Very interesting article. There’s something compelling about how little we know about the cold dark undisturbed places such as deep lake bottoms. Are there any completely pristine systems anywhere in the world so untouched that what we see now is what would have been seen when humans first arrived? With the exception of Antarctica, for obvious reasons, on all the continents it seems that every major river and lake has been subected to humans’ endeavors to harvest them. The most conspicuous examples of big and rich resources would be taken at the earliest opportunity, I suspect. So what we see now reflects the average thresh-hold for humans to find it worthwhile harvesting over a pretty long time. So the idea of an occasional population in the right condition and left undisturbed …or over-looked is more like it…sounds like a real if remote possibility and lately I like things that are remote. cheers

  13. mystery_man responds:

    One thing that is also interesting when considering overgrown crayfish is that there have been studies on the crayfish population in Lake Mashu. For example, in the study I mentioned in the article, there were hundreds of individuals captured, all of them of the signal crayfish species. There were no specimens of any other species caught in the snag nets. Also, of the adults measured, not a single one was larger than the maximum size known for signal crayfish.

    If there are overgrown signal crayfish in Lake Mashu, I would think that perhaps there would be some intermediate sizes, some larger than usual individuals turned up in the studies, but none were. Nothing pointed to overgrown crayfish. There was absolutely no evidence that any other species of crayfish is there either.

    This doesn’t mean that overgrown specimens or other exotics are not there, they could be lurking in other areas. However, there is a well sampled group of signal crayfish that are within known sizes in the lake, and then the giant crayfish that are a huge leap up in size for that species with no documented evidence that they are becoming overgrown and no sign of other species other than signal crayfish has been found there. Of course I’m not saying it is impossible, I’m just trying to get to what is really going on and offering information for your consideration.

    Perhaps there are very old, very large crayfish in Lake Mashu. I tend to think if there are, then they are perhaps not signal crayfish, but a larger species that has gotten absolutely huge in this environment, larger than any recorded in freshwater before. Some of the factors I mentioned in my article could be at work, or something else like just living a long time. Read the sizes I listed for this mystery crayfish and the sizes known for signal crayfish (as well as the sizes turned up in the studies), there is an enormous discrepancy. The ones reported in this freshwater lake are the size of extreme examples of marine lobsters.

    Certainly there are some factors at work in this lake, perhaps beyond just very old crayfish reaching sizes far beyond what is known for their species. It should also be remembered that there has been some evidence of neoteny in the crayfish, so this could be an important clue, as I mentioned in the article.

    Whatever the reason, I think it is an interesting cryptozoological mystery.

  14. mystery_man responds:

    Dogu4- Yes, that is exactly what interests me so much about this case as well. You have this population of crayfish that has been overlooked and mostly undisturbed, in an environment that is not its native one. It’s interesting to speculate about how this could turn out, and to what extent any of the possible factors, or what combination of factors mentioned by myself in the article or by other commenters here, could be playing a role in the development of these giant crayfish.

    By common knowledge, these giant crayfish should not be there in this lake, yet reports seem to indicate they just might be. Just what is going on in those cold, clear waters, is something I find fascinating to think about.

  15. HOOSIERHUNTER responds:

    There are two things that occur to me about the giant seen on the bottom of the lake.

    1) I don’t think your average crawldad (that’s what we call them here in Indiana) can take those kind of depths. I remember when Lake Monroe was put in as a reservoir in southern Indiana all the crawldads floating to the top that had lived in the creek beds. The pressure killed them.

    2) I wonder if the huge appearing specimen might have been a caused by magnification. Maybe it wasn’t so big (or so deep) and only appeared larger than it truly was due to the distortion of the light rays through the water.

  16. HOOSIERHUNTER responds:

    Oh, just for your information: Lake Monroe is only about 60-65 feet at its deepest.

  17. graybear responds:

    Another very interesting post, M_M, although being from the South I see the word crayfish and read the word crawdaddy. 🙂

    I very much enjoy the way you very fairly present both the pros and cons of your subject matter.

    I wonder, though, if you might not be missing a natural means of a crayfish sub species appearing in the lake. Crayfish reproduce by producing eggs, and in many if not all species of crayfish, the eggs can remain on the mother’s body for months before hatching out. It seems to me that in the 11,000 year history of the lake that a duck, goose, whatever might unknowingly have traveled from some nearby lake, stream, or pond with crayfish eggs nestled away in its feathers, and dropped them in the lake. This would have introduced crayfish into the lake, a small population which, lacking much genetic diversity, might easily encourage gigantism. A lot of farm ponds, completely isolated from any other water source, develop fish populations by just this method.

  18. mystery_man responds:

    Graybear- That’s an interesting idea. However, there are only three species of crayfish (crawdaddies 🙂 ) known to live in the wild in Japan, as I mentioned, and the largest of these is the signal crayfish that is already known to be in this lake. The other two crayfish species (one native to Japan, and the other the introduced Louisiana crayfish), are even smaller, so even if they had been added to the lake by the methods you mentioned, I’m not sure it would make much difference size wise. The signal crayfish is the largest known to be here in Japan, and it is well documented in Lake Mashu (if not at giant sizes), so that’s why I’m looking at it when I consider gigantism.

    Also, during the studies, no other species of crayfish was found to be there anyway. They were all signal crayfish. If it is an exotic species other than the three known to be in the wild in Japan, I would be more willing to think it was directly introduced to the lake through an irresponsible pet owner than add complexity to the problem by saying an exotic was released elsewhere, after which its eggs were transferred to the lake.

    HOOSIERHUNTER- The crayfish that was sighted on the bottom was not in particularly deep water. It was seen close to shore by a fisherman, certainly not in depths that would crush it. The lake doesn’t just drop down to shell crushing depths anyway, the crayfish could stay in shallower water. A large population of signal crayfish have been thriving in the lake since the 1930s, so its clear that the habitat in Lake Mashu can support them.

    Size distortion seems like a possibility for some of the sightings, but that would not explain the specimens that have been allegedly captured.

  19. springheeledjack responds:


  20. springheeledjack responds:

    I think kids are the same the world over 🙂 (referring to Kittenz’s comment). We have a creek near my grandmother’s place and my brother and I used to spend summer afternoons hunting crayfish. Now in Iowa they only get a couple-three inches in length, but still it was a summer hobby.

  21. Weezy responds:

    Very cool, I love stuff like this. Reminded me of the Giant Asian Hornet for some reason, which I also find fascinating.

  22. Sordes responds:

    Crayfish normally colonize new waters not by birds but by walking over land. When population becomes too dense, some indiviuals often leave their home-waters to look for new homes. This is a big problem if people buy crayfish for their ponds, because if they are already too large, they will often disappear.

    A note about gigantism: Thermoregulation has no importance to most aquatic cold-blooded (this does not refer to sharks, tunas and other ones which are actually possible to increase their body temperatures) species. If a lobster lives in a lake, it will always have exactly the same temperature. The water is all around it, it produces nearly no own additional warmth with its metabolism, so it has always the temperature of the water, no matter if it is a millimetre or a metre in length. Size is in this thing only important for terrestial animals and warm-blooded animals like whales. But there seems also some good reason to think that many animals are not just bigger in cold climates because it is colder, but also because there are richer sources of food, at least if you count marine food-sources like fish, squids and krill.

    Many people highly overestimate the possibilities of gigantism among species. There are always distinct borders, also for non-tetrapods and animals which grow for a long time.

    Introducing crayfish can be highly disatrous. In the late 19th century the American signal crayfish was introduced to parts of Europe. This species is a vector for a fungus which is lethal for European crayfish, and so they wiped out nearly all populations of the bigger Astacus astacus.

  23. cryptidsrus responds:

    I agree this makes for an interesting mystery.

    Good post, Mystery_Man. Why not do the Tengu next time, Brent???

    They’re “somewhat” cryptozoological. And VERY Japanese. 🙂

  24. mystery_man responds:

    Sordes- Thermoregulation through large size plays a part in many cold blooded animals, including marine ones, reptiles, and even large arthropods. Gigantothermy is in fact mostly seen as an adaptation in ectothermic animals as a method of more efficient heat regulation, so I’m not sure how you can say size is only of importance to warm blooded animals. Gigantothermy is largely a cold blooded adaptation.

    As for cold blooded aquatic or marine animals, it is not as simple as saying that since these animals are cold blooded, there is no warmth to be gotten from the water around them. If that were the case, cold blooded animals in the deep sea or very low temperatures would die. What you are overlooking is the warmth produced by muscle movement in the organism, which can produce some amount of heat even in cold blooded animals, and which in turn is managed through large size in the case of gigantothermy. Gigantism can be a factor for more efficient thermoregulation in aquatic or marine cold blooded organisms.

  25. Jeremy_Wells responds:

    I know those same “crawdads” kittenz mentioned from the Kentucky creeks and rivers. I used to catch them too. Usually they were pretty small (a couple inches). But after one of our seasonal spring floods we found a very large crawdad, whose body (tail and head, not claws) measured probably 7 inches or more, sparring with a neighbor’s dog in our backyard. The dog would bark and snip at it, and the crawdad would pinch at her nose, causing her to jump back and bark more. Dad eventually shooed the dog off and used a stick to direct the crawdad (which he described as looking like “a darn baby lobster”) back toward the creek. I’ve seen other large crawdads since then, but this one was definitely the biggest. A real “hoss” as my dad would say.

  26. mystery_man responds:

    Note that I do not mean to say ALL ectothermic animals, of course.

  27. Alligator responds:


    I’m willing to concede there could be some very large introduced crayfish in the lake. You touched on this but I wonder how much size distortion could have resulted. I am assuming the water is crystal clear. I also wonder about the surprise factor – when you see something you don’t expect, sometimes it registers on the brain larger than it really is – a little bit anyway. Still a 18 to 20 inch crawdad would be nothing to sneeze at.

    This discussion reminds of the 1959 bad (very bad) sci-fi classic “Teenagers From Outer Space.” The monster in the film was a giant crawdad 🙂 The MSTK3 version is awesome!

    Here’s a link to a picture.

  28. mystery_man responds:

    Sordes- I also thought I should point out that even besides cold blooded animals such as large sharks, tuna, and leatherback turtles, which all exhibit gigantothermy, or heat regulation through huge size, to some degree, it has been postulated as a cause for large sizes in many cold blooded invertebrates or arthropods as well. For instance, gigantothermy is thought to be a possible factor for the huge sizes seen in some deep sea animals or those present in very cold waters, such as giant squid, giant isopods, the huge Japanese spider crabs, and so on.

    As I mentioned in my article, it could help eliminate the need for constant movement and can help regulate temperatures even in habitats with no external heat source. For instance, the heat that is generated through movement and muscle activity is normally negligible for the purposes of thermoregulation in cold blooded animals, however through the physics of having huge sizes (lower surface area to mass ratio), the amount of this heat lost to the environment could be slowed and retained more efficiently. It is an adaptation that could possibly have merit even in an animal like the crayfish.

    At any rate, thermoregulation is merely one possible scenario I have put forth here for gigantism in the known crayfish of the lake. There are many other factors that may play a role, that I mentioned as well.

    I would not be so fast to write off gigantism as a possible factor in a case like this. While you say it is often overestimated, it would be likewise be unwise to underestimate it as a possible cause here as well. The possibilities are not necessarily as limited as you may think, and there are some spectacular examples of animals that have achieved greatly increased sizes in relation to related animals elsewhere. We cannot simply ignore the role gigantism can play in the evolution of some life forms under certain conditions. Insular gigantism is a well documented and important factor in the evolution of many island species, for instance.

    What I am trying to do here, with these giant crayfish, is investigate the possible reasons for it, and gigantism I feel is one possibility that needs to be looked at. The conditions in this lake could provide a variety of reasons for why these crayfish may have adapted some form of gigantism as a survival strategy, and so I feel it deserves some consideration.

    Alligator- I agree. I tend to think size distortion could play a role.The only thing is, the crayfish measured so far I would think are awfully small to be mistaken for crayfish that are 3 or more feet long, even under ideal conditions for distortion. Since crayfish are known in the lake, I don’t think people would be particularly surprised to see one there unless it was abnormally larger than usual. As you say, it would be still much larger than anything known in the lake and would be nothing to sneeze at. 😉

  29. flightsuit responds:

    This isn’t the first time one of these has cropped up in Japan…



  30. mystery_man responds:

    Sordes- One more thing on thermoregulation in aquatic cold blooded animals. Thermoregulation in aquatic animals is not only of importance, it is seen in such species already. There are several ways that aquatic cold blooded species can and do keep their body temperatures above that of the surrounding medium (in this case, water). These processes, or a combination of them, can be of use in trying to explain what is going on here with gigantothermy.

    More or less, a cold dwelling aquatic animal has to overcome two basic challenges in its environment concerning heat retention. It has to increase heat production and it has to minimize heat loss.

    Size is already an advantage to the latter, since a smaller animal is going to have trouble reaching temperatures much higher than the water due to their size and the conductivity of the surrounding water. As I have explained, a large size allows for a slower rate of heat loss to the environment, due to decreased surface area in relation to overall mass. It also leads to higher metabolic rates. This has been postulated as a factor of heat regulation in a wide variety of large aquatic animals such as colossal squid and in animals such as those exhibiting deep sea, or abyssal, gigantism. Cold water could be a factor leading to increasingly larger sizes as an adaptation in some species and research on fossils of ancient crustaceans has supported this to a degree.

    In addition to just size, aquatic cold blooded animals can regulate heat with efficient heat exchangers and blood circulation systems. Rates of heating and cooling can be influenced by circulation of the blood. Blood flow can be an enormous benefit to heat exchange, especially in a water environment, where the resistance to the heat exchange is low. An example of this can be seen in some fish such as tuna.

    As I have already stated, heat production itself can be caused by muscular activity, which in coordination with efficient minimizing of heat loss to the environment (such as huge sizes, blood circulation, and heat exchanger systems), can be helpful for thermoregulation in these aquatic ectothermic animals. The higher metabolic rates found in larger animals can contribute to this as well.

    In the case of crayfish in Lake Mashu, there could be another factor involved, the high oxygen content of the water. Some species of snakes, for instance, can raise their body temperatures while incubating their eggs. During this process, oxygen consumption skyrockets, which is caused by strong contractions of the muscles. These contractions are what causes the heat to rise, a similar effect to what happens when mammals shiver. For a cold blooded animal, it comes at a great energy cost, but it is still possible to raise the body temperature through such a process. If the Lake Mashu crayfish have free access to plentiful oxygen and food resources, it definitely seems that large size could play some sort of thermoregulatory role, and is a possible contributing factor to the size gains.

    On a final note, the difference between what is “cold blooded” and “warm blooded” is not always so cut and dried as is often thought. Many cold blooded animals can fall somewhere between the two extremes, and some can exhibit characteristics traditionally thought of as strictly in the realm of “warm blooded.”

    To say that thermoregulation is impossible or “of no importance” for aquatic cold blooded animals is greatly oversimplifying things and is not accurate anyway. Neither is it always possible to make broad sweeping statements about all cold blooded animals in general.

  31. mystery_man responds:

    As a matter of fact, there are so many categorizations for thermal regulation and heat production in animals, so many specific adaptations and strategies, that it’s hard to really classify any organism as simply “cold blooded” or “warm blooded.” There are many different gradients and those terms are actually rather vague. Many animals traditionally thought of as warm blooded are not even so easily defined as such anymore. It is not clear cut. As I said above, a lot of these animals fall somewhere between the two extremes of the traditional ideas of “cold blooded” and “warm blooded,” although I’ve used the term “cold blooded” for simplicity’s sake.

  32. Sordes responds:

    mysteryman, the problem is that water leads warmth much better than air, so an organism looses much more of its self-produced warmth than at land. If you swim in a lake your body will loose much more warmth than in air of the same temperature. If we look at terrestrial cold-blooded animals, you can actually see that in cold regions only small species live, whereas in warm climates big snakes, monitors, crocodiles or big tortoises can live. Bigger reptiles needs just too much time to recover from cold nights when there is only a moderately high temperature during the day.
    But in water it is again different. There are a lot of animals which have no problems to live in cold water even at comparably big sizes, for example giant japanese salamanders. But that´s also because they have no problem with this low temperatures, because their metabolisms are adapted to this, and very low. All the animals living in the deepsea have actually nearly exactly the same temperature as the surrounding water. Of course their metabolisms produce own warmth (I did not forgot it, I just wrote it is nearly nothing), but this is nearly nothing, and this warmth gets lost in the water, so their body size has nearly no effect on their body temperatures, especially at animals with very low metabolisms. There are surely much more important reasons for gigantism than only thermo-regulation, for example the availability of food, sexual competition, protection against predators and things like this. Animals like tunas are very different from normal cold-blooded animals, because they are actually more or less warm-blooded, as well as several sharks. This animals can produce a lot of warmth in their bodies, and in this cases a big body helps them to maintain high body temperatures, but that´s different.
    When I wrote about gigantism I did not mean gigantism which occured during evolution, I have no doubt that evolution can cause massive increasing of sizes. But I was talking about gigantism of single specimens within a species. Even a cold-blooded animal just can´t grow several times bigger than the known maximum sizes of its species.

  33. mystery_man responds:

    Sordes- That’s the whole point. It doesn’t matter how much sun there is or how cold the environment is for an organism with gigantothermy, and large sizes are how it works.

    Bigger sizes minimize the loss of accumulated body warmth into the environment, and this works underwater or in the deep sunless sea too. That’s the whole reason why gigantothermy, and all of the other ways these organisms deal with the cold water, would develop in the first place. Although the warmth produced in these animals is negligible, this heat can be accumulated and more efficiently kept within the body through things like huge sizes. Animals such as the leatherback turtle actually maintain a metabolism similar to warm blooded endotherms largely due to their size.

    The whole purpose of gigantothermy is keeping whatever heat is produced in the body from escaping, regardless of the water surrounding them. Large sharks maintain their warmth in great part due to their large sizes. In this case, size has everything to do with it because the warmth is retained due to the physics of lower surface area to overall volume. Size is the whole point of gigantorthermy, it makes a tremendous difference for heat regulation. Gigantism is not the only way, but it is one way to efficient heat retention in a cold water environment and it relies on size.

    I don’t know how I can illustrate any more plainly that large sizes plays a role in thermoregulatory adaptations like gigantothermy. I feel like my explanations are not getting across here.

    Gigantism is one strategy for dealing with the challenges of cold water environments, just as what you see with the mechanisms at work in tuna and some other cold water animals. Tuna are not warm blooded animals, they have adapted thermoregulatory mechanisms, including undoubtedly some benefits due to their large sizes. This is why they have these warm blooded characteristics, because of thermoregulation. I’m trying to point out here that they are not the only ones to do so. Any very large cold blooded animal with the right adaptations could similarly produce this warmth and keep it from being lost to the environment, including arthropods and invertebrates.

    Thermoregulation is not “of no importance” to cold blooded aquatic animals as you stated before, and gigantism is one possible way for animals to do this. That is what I’m trying to explain here. Cold water dwelling animals have shown a large range of adaptations and strategies for dealing with the problem of thermal regulation. Gigantism is one of them.

    I know about Japanese giant salamanders, I’ve actually researched these animals. Among other things, the principles of large sizes helping with thermal regulation may just play somewhat of a role with them as well.

    Also, all deep sea creatures actually do not necessarily have the exact same temperature as the surrounding water, and as I’ve been trying to say here many of them manage to maintain temperatures well above the surrounding water. As a matter of fact, in many cases, the smaller the animal, the more likely it will not have a substantially higher temperature because of how fast the heat is lost to the highly conductive water. This makes gigantothermy all the more relevant.

    Yes, gigantism can come about for many reasons. Thermoregulation is certainly not the only reason, or even the most common one. I did not mean to imply that, I’m merely trying to explain how it is possible and how it is worth considering here. Thermoregulation is one reason for gigantism, and it is a perfectly reasonable adaptation for an aquatic, cold blooded animal to develop. Size can affect heat loss to the environment. It’s not the only thermoregulatory method, but it is one possibility. I’ve been saying it is one possible reason for why these crayfish would get so large.

    I will say that I agree with you about just a few specimens within the species suddenly getting that incredibly large. This sort of thing I would expect to evolve over time. It is one thing that I even mentioned in my article here. It’s a strange case.

  34. Sordes responds:

    Mysteryman, it actually matters a lot a lot how much sun there is and how warm an environment is, especially for big cold-blooded animals. A small reptile like a lizard or snake will cool down during the night, so it has to warm its body in the sun. As it is small, it has proportionally much surface which can collect warmth from the sun, so it needs only comparably little time (and often still long enough) to reach a temperature which enables its organism to work in a fast way. But a big reptile would need much more time to warm up, because it has compared to its mass only much lesser surface area, in this aspect this is a big disadvantage and no advantage. You will now say that this doesn´t matter because they maintain more warmth cause of their bigger bodies. But even a big reptile looses much warmth during the night, especially in colder regions. Even crocs and komodo dragons need long sunbaths at the morning. A very big cold-blooded animal would actually need in a colder climate more time to warm its body in the sun than it had, because the days are not long enough. Furthermore nearly all cold-blooded animals lack a protection against loss of warmth like some kind of hair, feathers of fat-layer under the skin.
    Even warm-blooded animals loses extremely quickly their warmth when they have no isolation against the coldness. A crayfish has no isolation at all, and it has a very low metabolism anyway, so it produces only very very few own warmth which becomes lost nearly to 100% in cold water anyway. So gigantothermy is really no phenomen we should consider for such an animal.

  35. dogu4 responds:

    Thanks for these expansive and thorough examinations of aspects surrounding gigantism and thermoregulation. It’s plain to see that this is complex and reflects the fine grain detail onemight expect to be seen in this nexus of biophysiology and thermodynamics. It takes some attention (well spent, IMO) to integrate it into my ever evolving understanding of nature and its systems, so glad for its firm footing in fact and rationality…and extra points for keeping it culturally relative (Yeah, like so…What is it with the japanese and giant sea creatures? Like even their distinctly archetypical space alien imagery has tentacles and looks like an inverted sea aenenome with eyes and fangs..but subject for another post maybe).
    Might want to keep in mind regarding giganitism is the need for the giant organisms to be able to get enough oxygen and glycogen to the tissue, as well as dissapate heat. There is a physical limit to how distant from the circulatory system it can be, and so how big it could it would seem…but cold water under pressure holds a lot of oxygen and nutrients, and left unmolested nature will surprise us…with even more mystery. cheeres

  36. Allan Slavik responds:

    Wow, that lobster being held by the 16-year old boy looks like it could crush his skull with its pincers!

  37. mystery_man responds:

    Sordes- I’m not sure what you are trying to say. I am well aware of the principles of heat loss in animals. In most cases, yes, the heat in the environment is very important for most of these types of animals. I am not denying that. However, gigantism in regards to thermoregulation is a known phenomena that does happen, and is documented in nature, no matter how much you seem to want to deny its existence. It’s animal physiology 101 here. I do not think you are considering all of the information on animals such as invertebrates and crustaceans and others that all are thought to possibly regulate temperature in the very ways I am describing here. Even in the deep sea, with little or none of that sunlight you are talking about, where it is always cold, some animals may be utilizing this adaptation.

    Anyway, I never meant to say it was the only possibility here. It was one angle I was exploring, that you seemed to want to latch onto without really listening to my arguments. Gigantothermy, despite what you are saying, is a real process in a few animals similar to crayfish (such as giant isopods and crustaceans). But I fully admit it is perhaps not what is going on here. As you have pointed out and as I did as well in my article, there are a great many reasons why an animal can have gigantism. Any one of them may be contributing to what is going on in Lake Mashu.

    Thermoregulation is absolutely not the most important factor in size gain, and I can agree that it may have nothing to do with this case. However, whatever the factors in each species may be, just keep in mind that some of the largest aquatic cold blooded animals on Earth are cold water dwelling creatures. The largest invertebrates certainly are. The largest freshwater invertebrate on Earth is a type of crayfish that favors very cold water. So it seems important to me that when considering giant crayfish in this very cold lake, we should look at these examples when trying to figure out what is going on.

    Considering the tendency for some cold water animals to be very large, I am trying to examine the possibilities with this crayfish that has been reported. Gigantothermy was merely one, and granted possibly not even the most important, factor.

  38. mystery_man responds:

    Sordes- Since you mentioned it, I also thought I would mention the process of gigantothermy in relation to the tropics, even though I really did not want this to become a big discussion on this.

    With regards to the tropical habitat of the monitor lizards, komodo dragons, and other large cold blooded animals, the same principles of large body sizes can apply when looking at heat gain and heat loss. Large body sizes are of use for thermoregulation in these environments as well. It all comes down to the physics of body dimensions again. It’s not just about amount of surface area in these animals, but rather more accurately the ratio of that surface area in relation to overall body volume.

    For instance, the small lizard you mentioned. Yes, it gathers heat more quickly than a large reptile, but what you are overlooking is that is also loses that accumulated heat more quickly as well. A larger reptile takes a longer time to gather heat than a smaller one, but it also loses that heat at a slower pace. This can absolutely be an advantage for a couple of reasons.

    For one, since gigantism slows the amount of heat absorbed from the environment, it can also help to minimize the effects of overheating in animals in the heat of the tropics. The example you gave of these large reptiles gaining heat more slowly proves my point in this case. Second, the same way that gigantism can minimize heat loss in cold environments, it could also limit the effects of cold periods. During the cold nights, for example, the larger reptile will lose comparatively less heat that it has absorbed during the day than a smaller reptile. What you don’t seem to understand is that yes, large reptiles lose a lot of heat during the night, but the point is they lose relatively less of it in relation to their overall mass than a smaller reptile. In these ways, large body sizes can be an advantage even in the heat of the tropics, rather than “no advantage” as you say.

    The behavior of the tropical large reptiles can also be seen as a factor in relation to their environment. Large tropical reptiles are typically less active, and will spend a long amount of time gathering heat from the environment as you said, yet they are less likely to overheat in this environment, and they lose that heat more slowly during cold times such as night time.

    Hopefully you can somewhat see how gigantism can provide thermoregulatory benefits the same way in the tropics as it can in cold water environments. Large body sizes are not only a possible cold environment advantage, but they can be a hot environment advantage as well. In cold environments, the little heat they do get is retained more efficiently, and in hot habitats, the benefit can stem from that and the fact that the amount of heat absorption is slowed. The effect might not always be great, but it could be one benefit to large body sizes.

    It’s physics. Regardless of helpful insulating factors such as fur and feathers, larger volume to surface area simply loses heat and gains heat more slowly, and this could be an advantage for some animals in both cold and hot. In cold water environments, the heat is not necessarily external, but can be produced by internal means such as muscle movement. Tuna and sharks are constantly moving, which produces heat that is thermoregulated by their large sizes and unique circulatory systems. This is exactly what I am saying in why animals in a cold environment with less time or opportunity to gain heat from the sun and environment could see a benefit to their large size. It keeps what little heat they can produce within their bodies, and any small benefit can be of importance in nature.

    On the other hand, in the tropics the heat is gathered from the sun and warmth of the environment, which is gained more slowly (keeping down overheating) and lost more slowly (during the night) due to large sizes. This could be a benefit as well for the reasons I mentioned earlier such as preventing overheating and carrying the animal more efficiently through cold times. I suppose it could even possibly be a disadvantage in the sense that too much activity in large tropical reptiles could actually hypothetically cause them to overheat. However, as I said, there are benefits to be had as well.

    My whole point here is that gigantism can be an adaptation for tropical environments for the same underlying reasons it is for cold environments. Of course it is not some magical cure for the disadvantages and challenges inherit in cold blooded animals, but neither is it of “no use,” or “no importance” as you seem to think.

    Anyway, yes I agree that gigantothermy is not the biggest driving factor behind gigantism in cold blooded animals. I’m just trying to illustrate possible benefits and how it works.

  39. mystery_man responds:

    Sordes- To sum up my thoughts, I must say that I do agree with you on some points more than you may think.

    For instance, I also don’t believe that thermoregulation in and of itself is necessarily a significant reason for organisms to evolve gigantism. There are many other more important factors that can lead to this adaptation, and thermoregulation was one possible co-contributing factor I was exploring. I actually think that in many if not most cases, any possible thermoregulatory advantages of gigantism are likely mostly a spin off benefit of sizes gained due to other reasons. In other words, for some animals, it is a bonus rather than the whole reason why they got so big to begin with. Most large cold blooded animals no doubt originally evolved their sizes due to other selective pressures and any added benefits are just icing on the cake. In the end, gigantothermy and its exact role in the evolution of large sizes in cold blooded animals is not really fully understood and is definitely debatable.

    I also agree with you that it would be strange to see any sort of gigantism just pop up within a species in such a short time among just a few individuals in this habitat. This is especially odd considering no other specimens of particularly large size have been turned up in studies of the crayfish population of the lake.

    In the end, gigantothermy is just one factor of many I considered here, and in fact it is not even my main hypothesis for this particular animal. I did not mean to sound like I thought that this would be the only reason for the crayfish to get that big.

    I did not mean this to become a long debate on thermoregulation in cold blooded animals, as fascinating as it is. The main point with my speculation was to fuel a discussion on “what could possibly be behind the alleged abnormally enormous crayfish reported in this lake?”

    That is the spirit of this article. Anyway, your input is appreciated.

  40. Sordes responds:

    I did not oversee the fact that big cold-blooded animals don´t lose their warmth as fast as smaller animals. But this count only to a distinct degree, because they lose a lot of their warmth too. This can help in warm climates when the day is very warm and the nights are still warm, but this doesn´t work in colder climates very well, because even a big cold-blooded animal will loses nearly 100% of its gathered warmth of the day during the night and would need too much time to gather sunwarmth during the day.
    And in the water it is even lesser effective. Water absorbs much more warmth than air, and gigantothermie makes only sense if an animal produces a lot of warmth. This is surely the case in animals like swordfish and tunas (note that they still prefer warmer waters anyway), because their metabolism is possible to produce a lot of warmth with muscle activity. Bumblebees are also able to increase their warmth significiantly with the muscles of their wings, but for this reason they posses also a “pelt” which acts as a thermoisolation. But cold-blooded animals in the water which don´t produce much warmth with their metabolisms can´t profit from gigantothermy unless they are really very big. In crustaceens like crayfish we have low metabolisms which produces little warmth anyway, we have no kind of isolation which would prevent loss of warmth and they are completely surrounded by water. I find it also interesting that the largest species don´t live in cold climates, but in warm climates like Australia and Tasmania…
    Most cold-blooded animals which live in cold water have anyway very low metabolisms, and their heat production is minimal, especially deepsea species. There is simply no warmth which would be saved by a bigger body. Their whole organisms are adapted to low temperatures with enzymes and other body functions which can work at very low temperatures, in some cases even at freezing temperatures. We can´t do this, we are warm-blooded and can´t long survive under such conditions, so humans can very quickly die in cold water.

  41. mystery_man responds:

    Sordes- The largest species do live in cold climates. I wish you would research this before coming here and saying such things. The Tasmanian giant freshwater crayfish, which is the largest freshwater invertebrate, lives in cold water habitats. Do you think that everywhere in Australia and tasmania is a tropical warm environment? Most crayfish species do. For example the second largest, the Murray crayfish, as well as the signal crayfish and the Japanese crayfish, which only lives in the northernmost, coldest parts of Japan. In fact, warmer water can actually kill them.

    Shall I go on? The world’s largest salamanders, the Chinese and Japanese giant salamanders, live in cold water. The giant spider crabs which are among the largest of crabs, live in cold water. The giant squid and colossal squid, the largest squid, live in deep, cold water, as do many of the largest octopi and the giant deep sea isopods I mentioned. Many large sharks thrive in cold water environments, and a lot of the largest freshwater fish prefer cold water as well, as well as many large saltwater fish. The tuna you mention actually thrive quite well in cold, oxygen rich waters. I’m actually having trouble of thinking of too many types of warm climate cold blooded animals that are a whole lot larger than their cold water counterparts. Just what exactly do you mean when you say “actually the largest species don’t live in cold climates”? This is simply not true at all. Some of the world’s largest aquatic cold blooded animals live in cold environments. I really don’t see where you are getting your ideas.

    You also seem to be denying outright the possibility of gigantothermy in deep sea or cold water organisms, even though it is supported by a good deal of evidence and hypotheses within the scientific community, which you don’t seem to want to hear about. I know about the heat conductive properties of water and the challenges of cold water creatures, perhaps more than you seem to think I do. I am well aware of the physiological reasons for heat loss and heat gain, as well as thermoregulatory strategies and what is needed for cold blooded animals to survive.

    I’ve tried to explain how gigantothermy works or might work here. It is not useless to consider, and honestly some of your assumptions about the regulatory processes involved here are not completely accurate. Leatherback turtles for example do not have naturally high metabolisms either, they are not fast moving active animals, but rather are able to generate a high metabolism through heat regulation largely caused by the physics of simply being huge.

    You are also making statements such as “large cold blooded creatures lose all of their heat at night,” which is not necessarily true, and without considering that the smaller creatures lose it even faster. Once again I’ll say it, large animals lose their warmth they have accumulated during the day more slowly, which by definition minimizes the heat loss you are talking about and could make large sizes a benefit. Large sizes can help, they certainly aren’t completely useless for thermoregulation.

    Also, in cold environments, these animals can burrow or do a variety of other things to further retain the heat. You make it sound as if these reptiles would spend all that time gathering their heat and then go sit in the coldest place they cay find, which is not necessarily what happens. You are using the very most extreme examples of what could happen without looking at how the processes I am explaining could help lessen that negative effect. I stand by what I said, they gain heat and lose heat more slowly, which can have dual benefits.

    Anyway, the most important thing here is that indeed many of the largest cold blooded aquatic animals do live in cold environments. This is of importance to the topic of these giant crayfish.

  42. mystery_man responds:

    Of course by “largest species” in the first sentence of my post above, I meant “largest aquatic cold blooded species,” which is what I was talking about before when I said the largest aquatic cold blooded species live in cold environments. Just to be clear, I am talking about the tendency for some of the largest cold blooded aquatic animals to live in cold water environments, for whatever reasons. This is relevant to the discussion on these crayfish.

  43. Sordes responds:

    mystery_man, of course I know that the waters in which the giant tasmanian and australian crayfish life are comparably cold, but anyway, why are there for example no similar sized crayfish in northern scandinavia where also crayfish live? Even considering the fact that the australian and tasmanian waters in which this giant crayfish live is in general cold, the overall climate in those regions is still much better than let´s say in norther Sweden, and even a fast stream will most probably have warmer water in average than in colder regions. The big problem of many crayfish with warm water is also not the water itself, but the lower oxygen levels.
    Your argument with animals like the giant salamander actually don´t work. You mention some very big animals which live in cold water, but this shows not the slightest indication that this has anything to do with gigantothermie. One reason for the existance of many big marine animals in cold water is most probably the rich resource of plancton and baitfish, and not a hypothetical advantage of a warmer body. Warm seas are often poor in plancton, for example the mediterranean sea whereas cold and oxygen-rich seas like the atlantic ocean are full of fish. And as I already wrote before, those animals which live in cold water don´t need additional warmth anyway. Amphibians are often much better adapted to cold climates than reptiles, some of them even begin to mate when the surface of lakes and ponds is still frozen in spring. This includes even small species like toads, which seems to go quite well in cold water. Actually nearly all amphibians in non-tropical regions are quite small compared to the large tropical frogs and toads. The chinese and japanese salamanders are special in this case. They live in cold streams, but this doesn´t mean that this has anything to do with their body size. This is more probably an ecological adaption, and they are the biggest predators in their ecosystems. The giant squids, colossal squids and the other animals you counted live actually in cold water, but, and this is much more important, in cold and food-rich water.
    I would be very interested to see where you have seen any indication for gigantothermie in deepsea animals. Most deepsea animals are small anyway, and nearly all of them have very low metabolisms and lack any isolation anyway. So even for the bigger ones there is nearly no possibility to produce much metabolic warmth at all, and they lose it also very fast. They can´t take a sunbath as a lizard on land or even a turtle on the surface. They just have the same body temperatures as the surrounding water. Even if we consider that big animals will most probably have a body temperature which is often a little bit over those of smaller cold-blooded animals (I don´t deny this), this has only a minimal effect and is surely no reason for evolving larger body sizes. Large body sizes as prevention against cold water make only sense, if the body can lose a lot of temperature. Birds and mammals can lose very much warmth in the water, and big body sizes surely help in combination with thick furs, dense feathers and fat-layers under the skin to protect them.

  44. mystery_man responds:

    Sordes- My point is not that cold water animals like giant salamanders or all of the large animals I mentioned have anything to do with gigantothermy. Please read what I said earlier. I was actually saying, even agreeing with you, that gigantothermy may not be a factor in many cases. I also agree with you that it is not necessarily the most important factor, and that there are many reasons for animals to get to large sizes. Look at what I said-

    Thermoregulation is absolutely not the most important factor in size gain, and I can agree that it may have nothing to do with this case. However, whatever the factors in each species may be, just keep in mind that some of the largest aquatic cold blooded animals on Earth are cold water dwelling creatures. The largest invertebrates certainly are. The largest freshwater invertebrate on Earth is a type of crayfish that favors very cold water. So it seems important to me that when considering giant crayfish in this very cold lake, we should look at these examples when trying to figure out what is going on.

    Considering the tendency for some cold water animals to be very large, I am trying to examine the possibilities with this crayfish that has been reported. Gigantothermy was merely one, and granted possibly not even the most important, factor.

    What I was trying to point out here is that there are many ecological factors at work and I am looking at possibilities. Gigantothermy may be a bonus for some, but not necessarily all. I am not saying that giant squid and salamanders got that way due to gigantothermy, I wish you had read what I said more carefully. I am rather merely pointing out that many aquatic cold blooded animals are some of the largest of their kind due to a variety of reasons that should be considered for these giant Japanese crayfish. I am actually trying to look past gigantothermy here, that’s the point.

    Also, the oxygen levels I have already mentioned as a possible factor on many occasions in this discussion, and in the article, but you don’t seem to have listened to me and you mention them here as if it is the first time. Did you not read when I was talking about the role of high oxygen levels?

    I have clearly stated here that gigantothermy is little understood, and its exact range of effects is not totally known. It may play a small role or no role at all depending on the type of animal, but it certainly should not be entirely dismissed either. I do understand, and have even said here, that it is not always the sole reason for evolving large sizes.

    I will say that as we learn more about the physiology of these animals, the more lines between what is “cold blooded” and “warm blooded” become less clear and less easily defined. It is not always as simple as your arguments make it sound. Our understanding of these terms has changed drastically in recent years, and we are learning more. There are a wide range of thermoregulatory measures, strategies, and adaptations in animals, many that are poorly understood, and it is hard to neatly categorize animals and their thermoregulatory processes. A lot of animals lie somewhere between the two extremes. I would suggest keeping this in mind before make broad generalizations about what “cold blooded” animals or “warm blooded” animals can or can’t do based on these vague definitions.

  45. mystery_man responds:

    I also wanted to say that yes, dee sea gigantism in slow metabolism animals might play a minimal role, especially if there is no constant muscle movement or other heat source such as undersea thermal vents. That is likely correct to an extent.

    However, it is not fully understood what role gigantothermy could play in the deep sea animals that are very large, or exhibit abyssal gigantism, so it is one possibility I leave open.

  46. mystery_man responds:

    Sordes- One more thing I wanted to point out is that your question of “why are there for example no similar sized crayfish in northern scandinavia where also crayfish live?” is a red herring. What I am saying is that it is possible for crayfish to reach such large sizes and that the ones that do live in very cold water similar to the conditions in northern Japan. Just because they are not in Scandinavia does not mean they don’t exist anywhere.

    Also, there are certain temperature limits depending on the species of crayfish. I did not say that there were no limits to how cold or how warm they can tolerate. For example, the introduced signal crayfish in Japan can tolerate warmer water temperatures than the native Japanese crayfish, which needs lower temperatures. It depends on the species. For some, like the Japanese crayfish, warmer water can kill them. Of course oxygen level is one of the factors there, I did not say it wasn’t. The lack of oxygen is a quality of the water itself. It does not matter what the reason is, the point is that depending on the species, there are limits to the water temperatures they can tolerate. Saying that it “is the oxygen level rather than the water itself” doesn’t make any difference on this main point.

    Besides, we are not talking about Scandinavian crayfish. Perhaps those environments are simply too cold for that large species. As I said, there are limits depending on the species. However, signal crayfish in lake Mashu, Hokkaido, are thriving. The temperatures there are similar to those tolerated by giant cold water crayfish such as the Tasmanian freshwater crayfish. Tasmanian freshwater crayfish need cold water to survive, which is similar to the crayfish that are found in the cold, northernmost parts of Japan. Of course I’m going to consider the possibilities of similar factors at work. Why shouldn’t I based on the argument that they are not found in Scandinavia? There are a lot of reasons why giant crayfish might not be found there. Does that mean I should dismiss all of the possibilities?

  47. jedimaster5000 responds:

    Animals of the sea, or most large bodies of water are large because there is lots of Oxygen, and a lot of it, from it. (I read some article about it, thats why in the Silurian era and of course sometimes afterwards animals like insects were gigantic).

    Anyway, its amazing finding something like this. but what is much more better are fishes, which btw, never stops growing, like humans do (the more older they are the bigger then get, and thats probably the same w/ crustaceans)

  48. mystery_man responds:

    Right, oxygen is very important. That was my whole point with mentioning all of the large aquatic animals that live in cold, highly oxygenated water. I have been mentioning this factor at several points. I do not mean to imply that the cold water causes gigantism all by itself, as some here seem to think, but the highly oxygenated water certainly doesn’t hurt. It is one factor that seems to help some organisms to get so large. The oxygen is conducive to the process, and without high levels of it, the animal might not be able to get so big. All of the examples I mentioned gain a benefit from the oxygen, even the giant salamanders absorb the oxygen from the water through their skin. Many of the largest examples of amphibians, crustaceans, fish, and so on, live in cold water and this is of course due to the high oxygen levels that they require.

    So oxygen doesn’t cause gigantism or huge sizes, I certainly don’t think that you are going to necessarily find giant creatures in every single cold, highly oxygenated environment. Many smaller animals require high oxygen levels too. Like has been mentioned here, there are many factors that can lead to the evolution of gigantism, and depending on ecological stresses, it is not a given that it will occur. But these high oxygen levels could help remove physical oxygen restrictions and be a contributing factor to allowing the organism achieve these large sizes.

  49. Redprat responds:

    It’s a pity that last picture was manipulated… Being from South Africa and in Cape Town, that is the typical lobster we get here. (colour, shape, but definitely not size)

    But look at the guy’s fingers… Compared to the lobster that would be about 25cm, and they don’t get much bigger than that. The reason probably as they don’t grow very deep, probably 10 meters down, and the resource is almost depleted. That’s why they are about $35 in a restaurant for one single tail, in comparison with a very descent size steak which would be less than $11. But on the black market which is in every small fishing town on our West Coast you could pick up a whole and mostly alive lobster for about $4.

    Pity, but we can wish.

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