I’ve been to the lake on many occasions but sadly have never seen Takitaro. It’s a very difficult lake to get to even hiking. I live in Colorado now and hiking the mountains of Japan was much more difficult due to the steepness, foliage, and wet weather. Asahi is a very rural area and the only road that leads up to the lake is very narrow and long passing through many old villages and tunnels. It’s beautiful. A true wilderness in Japan.

There are so many tales of the fish sighting, ghosts, and other creatures up there and the area is so remote, I wouldn’t doubt any of them. I still have many friends in Asahi and go back whenever I get the chance. It’s by far my favorite place in Japan.

I think another factor that we could be dealing with here is the oxygen level in the lake, which is to some extent linked to the temperatures present. Otori-ike has cold, highly oxygenated water, which can infer an advantage in organisms by providing them with plentiful energy reserves. This may also have an effect on size in the lake in conjunction with the food availability and other factors.

As I mentioned, these variables don’t exist in a void, they are all tied together, and perhaps made more “simplified” and acute by limitations of the smaller habitat. Rather than looking at just one factor when addressing the size of Takitaro, I prefer to look at the overall picture, and the way all of these dynamics are interacting to perhaps produce what is being reported in this locale. The interplay between these things in somewhat limited island and likewise lake ecosystems is what really draws me to cases like the Takitaro, and indeed island wildlife in general (which is where most of my professional interest is.)

Anyway, yes there are many unique possibilities for a remote, isolated environment such as this. For now, I am more or less trying to look at how these pressures and constraints we’ve been discussing, or lack thereof, are interacting within this isolated lake in the context of the known species and their apparent population densities.

Still, I agree there is room for the hypothesizing of other factors such as oxygen content and chemical make-up of the water. I greatly enjoy speculative biology, so you’re not going to get much argument from me there.

Who knows, maybe some unique, currently undescribed or little understood process could be uncovered at work in this particular lake. Stranger things have happened.

For instance other factors to consider are predation, amount of geographic isolation, and the level of competition present in the habitat, and these all have an effect on each other to some extent. Food availability can influence genetics, habitat size effects food availability and predatory pressures, and so on. For example in the case of competition, this can have an effect of the food availability, which over time could be expressed at a genetic level (such as gigantism and other adaptations) due to evolving traits to deal with these pressures.

The size of the habitat can have an impact on all of these things. Where these factors are all present in large habitats as well, they are more profoundly expressed in a smaller one such as an island or lake. Each of these variables is simply more acutely felt in a smaller habitat. You can imagine it like throwing a stone in a lake. If you throw it in a large lake, the ripples are not so significant whereas in a small pond they are more profound. The same goes for changing variables within a confined ecosystem such as a lake or island.

This is why you can see curious evolutionary strategies such as gigantism, dwarfism, and others depending on the specific pressures present. The factors you mention are having a more significant and immediate effect on the organisms inhabiting these smaller habitats.

In terms of evolution, the limited size of the habitat can cause the change in balance of these factors such as food availability and so on to favor certain radical evolutionary steps, such as the insular gigantism and dwarfism that I mentioned. It can create a situation where you have a more pronounced evolutionary “arms race” so to speak.

On top of this, there is even more to think about than just size in island ecosystem. The degree of geographic isolation of islands and lakes also means that you have this all going on in seclusion.

The combination of all of these things can lead to some pretty interesting adaptations in species compared to their continental relatives. In islands and isolated lakes we can find a good amount of unique, endemic species, all shaped by the unique circumstances and increased (or decreased) pressures directly related to their limited habitat size.

I think islands and lakes like this present a great microcosm for studying the effects of these evolutionary pressures and how animals adapt to them.

I would agree that islands and lakes are places where we can often find unusual evolutionary strategies and interaction of ecological variables. In the case of Otori-ike, perhaps there is something going on that we are unaware of, some factor that we have not even considered yet.

It’s interesting to think about.

If these fish are indeed real, and indeed as large as is reported, then something is going on. I think we have both established that gigantism is not likely. And the habitat seems like it is too small and populated by predatory salmonoids to offer a really robust food sources that could account for large sizes. Even if there were such food resources, I’m not sure that can explain the enormous sizes beyond what is currently known for these species.

I tend to think that we are dealing with a species not known to be in the lake, such as Sakhalin taimen, an unknown, or even your proposed Silurus.

Such large fish in this environment would certainly be odd, and not what I would expect to find here.

Thanks for joining the discussion and adding your insights.

The availability of food seems good in this lake to the best of my knowledge, but there is a lot of competition, which like in the case of sticklebacks, would limit any capacity for gigantism. I think it would limit any sort of large growth overall.

I think the only reason gigantism has ever really been brought up at all in relation to the Takitaro is because of the uncommonly large Dolly Varden that were caught in the lake. It has been one possibility brought up, however I really do think an unlikely one.

But you are right with regards to food availability. This is certainly a factor determining growth, and has an effect on size even when it is not necessarily an evolutionary trait that has established itself in the species at any genetic level.

Evolutionary trends or not, I don’t see much that leads me to beleive that we would have super sized specimens of any given species in this environment.

Anyway, thanks for the input and I am pleased you liked my article.

As I mentioned in the article, I too think gigantism is not a good possibility here, which is what I was trying to convey with that example. With the predatory salmonoid fishes, I would expect that they would in fact be more likely to even be smaller due to the incredible amount of interspecific competition that appears to be present in this lake, which of course would have an impact on food availability.

To balance out the whole insular gigantism argument, it is also important to remember the concept of insular dwarfism, which is what will happen when more rather than fewer restrictions on food supply and competitive pressures occur in the island habitat. Often larger animals, especially predators, will become smaller over time under these conditions. In this case, predatory animals often exhibit dwarfism rather than gigantism. So this has bearing when considering the possibilities. The lake in question does not display the lack of pressures that would be likely present in order for even guppies to display gigantism, so giant salmonoids indeed seem unlikely.

One thing, though is that many of the competitors were introduced here by humans well after geological formation of this lake. Perhaps something native to the lake had evolved to be larger somehow long before the addition of these new factors.

So yes, this is an isolated ecosystem. I believe there are good food resources there, however. There are self sustaining populations of smaller fish in the lake, and of course the predatory fish such as the trout and salmon are going to feed off of each other as well.

The thing is that this sort of fierce competition is going to most probably limit the size of the fish here. You may get a few that reach a ripe old age and get sort of a grand daddy fish out there, but the Takitaro sizes are far larger than any sort of fish known to be there.

Anyway, there is plenty to eat there for fish as big as these things are reported to get.

I think you are right in that we have here a good opportunity here in this relatively small lake, or “microcosm” as you put it so well. There is less area to cover and therefore a better chance of maybe finding something.

Sadly, I’ve never been to this particular lake, but if I had the time and resources, I might just try it myself. Maybe if I had help. If you’re ever in Japan and need a hand, you know who to ask.

Thanks for the kind words about the article. I truly am committed to providing good English language overviews to these cryptids. There is surprisingly little in English available on these creatures, so I hope I am providing something useful here.

Korollocke- Wow, that sounds amazing. In all of the time I’ve been investigating Japanese cryptids, I’ve never actually seen one.

By the way, I’ve been to lake Ikeda. I didn’t see Ishii either.