The adaptable fish myth?

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Sploke

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So I feel like starting a fight.... *ahem* intelligent discussion about the myth that fish grow to the size of their enclosures.

Now, I know that, as that statement stands, there's no logical backup for the theory. Just because you keep an oscar in a 10 gallon tank, does not mean it will stay 3 inches for the rest of its life.

However, in the wild we do see evidence of animals, mostly fish and reptiles, generally not mammals, adapting to the availability of some limiting resource, a common one being food. I was talking about this with a fellow fishkeeper who has been out of the hobby for some 15 or 20 years, and he is constantly amazed by the advancements that have been made in the hobby (i.e. I keep my betta in a 10gal community setup, and it works great. Apparently 20 years ago, this was unheard of.) He posed an interesting question, that in the wild, how do you suggest solid adult size for a fish? Take a largemouth bass for example. How big is an adult bass? It depends on a lot of things, a big variable being area of the country, among other things. Up here in New England, a 5lb bass is a pretty good catch. I'm no great fisherman, but I call it a successful day if I can land a few over 12-16". Now, a 14" largemouth and a 24" largemouth can probably both be considered adults. Go down south, and you'll see much bigger fish being caught on a regular basis. This could be attributed to a longer growing season, and more time to eat and get big and healthy. Would this be an example of a fish adapting to its surroundings? I would say yes. Fish that don't have as much time or as much available food to grow, stay smaller within a reasonable range. Is that to say that the 14" bass is unhealthy or not thriving? I don't think so.

Now, whether this is carried over to the home aquarium is what is under question. Since most of us keep tropical fish, they eat year round, there are no growing seasons/dormant seasons. However (and I'm not suggesting anyone starve their fish in an effort to stop growth), by paying closer attention to diet in our fish, is it possible that there is a certain limit to how big a fish will grow in the home aquarium? There is a lot of evidence showing that many species of fish grow bigger in the wild than they ever have in captivity. Does this mean we are screwing something up along the way, or is the fish responding and adapting to its conditions?

Just some thoughts I've been having, I'm not advocating drastic changes in fishkeeping for anyone, but I am curious to hear what opinions people have on the matter. Thanks for reading.
 

Wishful

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You also seem to be talking about fish of the same species in different geographical areas being different sizes. In that case, it isn't that an individual fish doesn't grow to a particular size, it's that the population of fish over time have adapated to their environment and evolved into larger/smaller fish.

The hypothetical aquarium oscar is only a single generation. Any significant variance from normal sizes would indicate stunting and be maladaptive.

Now, take that hypothetical aquarium oscar and start a breeding program in which you keep all the oscars in undersized tanks. Assuming you could get them to live and breed successfully (a big if), the most successful breeders would be those who best adapted to the conditions, they would, in time, pass those traits on to their offspring. But we're talking ALOT of generations
and even then you may well end up with very non-hardy fish that are only marginally successful.

Your game fish is a good example. The true test would be to take fry from one location and raise them in another and see if they adapted smaller without affecting their health (growing larger really isn't much of a test as most fish will happily and healthily grow larger if given greater than normal resources).
 

Rowangel

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I agree with Wishful.

The idea of ‘adaptability’ seems to be two ideas here. The example of bass adjusting to his environment shows quite nicely the ‘adaptability’ of a species over a long period of time and many generations. Not quite the same as the idea of throwing a fish into a small tank and expecting its genetic disposition to ‘adapt’ over the course of its life to fit to a smaller environment. Any adapting in this case would most likely involved stunted growth that causes damage to internal organs and a shortened life span. The idea that a fish will not grow as big with less food or room is akin to saying a child will not grow as fast with less food and room. Possibly true, but in this case the child will not be healthy, unlike the 14” bass who had generations of natural selection to adapt and can thrive nicely at that level. I would further say that the adaptability of a fish also depends on species and individual vigor, not just amount of food and space.

sploke said:
Now, whether this is carried over to the home aquarium is what is under question. Since most of us keep tropical fish, they eat year round, there are no growing seasons/dormant seasons. However (and I'm not suggesting anyone starve their fish in an effort to stop growth), by paying closer attention to diet in our fish, is it possible that there is a certain limit to how big a fish will grow in the home aquarium? There is a lot of evidence showing that many species of fish grow bigger in the wild than they ever have in captivity. Does this mean we are screwing something up along the way, or is the fish responding and adapting to its conditions?

So much that is natural to a fish is lost in the captive keeping (natural water changes from flooding/rain, change in seasons, variety of diet, migration and vast areas for movement and breeding selection) that it is hard to compare a wild fish left unencumbered to a captive bred or even wild caught/captive raised fish. I am not surprised that wild fish are larger than captive fish, they have far better environments that even the most well-meaning hobbyist can provide. Any evidence that a fish can be limited in its size from what is normal, IMO, is an indication that the fish is not being properly housed and/or fed the right foods, not that it is ‘adapting’ to the size of it’s tank.

Just my thought… ;)
 
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Sploke

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Ok, so maybe the regional differences was a bad example. But even in the same area, you get some adult fish that are bigger than others, of all different species.

Also, like I said, mammals don't seem to be able to adapt to adverse conditions as well as fish do. Here in CT, deer starve to death every winter because of a lack of food and overpopulation. Even with an overpopulation of fish, you rarely see a large fish die-off from something other than an external event (poisoning, large temp shift, etc.)
 

nerdyguy83

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Hate to just say "You're wrong" flat out, but the fact is that mammals are the most adaptable class of organisms on the face of the earth. Deer dying every year because of overpopulation isn't a maladaption. It is actually a sign that the deer have adapted so well the the spring and summertime environment that they can breed at will and produce so many offspring that they exceed the carrying capacity of the area in winter. Producing as large a number of offspring as possible is the natural way of having the most number of offspring alive come next spring. Deer obviously can't estimate the population size that the region can support and then practice population control amongst themselves. They meet the problem head on by simply making as many babies as possible and then letting nature do its work to weed out those ill-adapted to the conditions. Those that survive are obviously the strongest and future generations of deer are better for it. This is natural selection at work before our eyes.

To bring this back to fish so I don't look like a complete thread hijacker, the largest fish in a pond doesn't die because to get that big, he obviously had to be the best food-getter in the bunch. He is the equivalent of that line of deer that don't starve to death in the winter because they are the best adapted to the environment. I bet if you found the deer that starve to death this winter, it will be the smaller ones ill-prepared for competition.
 

Rowangel

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sploke said:
Also, like I said, mammals don't seem to be able to adapt to adverse conditions as well as fish do. Here in CT, deer starve to death every winter because of a lack of food and overpopulation. Even with an overpopulation of fish, you rarely see a large fish die-off from something other than an external event (poisoning, large temp shift, etc.)
Hum, interesting idea, but again a difficult comparison to make. It's hard to over-look (or smell) a bunch of dead deer. Mostly because they are so large, numerous and lack a lot of natural predators to take care of the corpses. However in a 'fish eat fish' environment it would be hard to track actual numbers of fish fatalities. Most fish, as you can observe in your own tank at home, have no moral issues with eating their own hurt/injured brethren should the opportunity arise. And in a hungry environment as you point out, this would make it near impossible to know what types of dye-offs might occur in an environment full of predators. A lack of fish corpses may not mean a lack of massive fish death.

In other words, this is not proof that fish are more adaptable than a deer, only that it is harder to track the cycle of fish than a large, visually obvious mammal.
 
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Rbishop

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Still thinking on the fish issue...though in the wild there are a lot of factors we cannot see and account for. In the home aquaria a lot of what we do could be detrimental in the small space, pollutants mainly.

Growing bigger fish down South, in general is probably true or do they get bigger faster? You should see how small the deer and squirrel are here in NC! Adaptation to low food supply because of high heat?
 

stingray4540

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I really like your argument sploke. It is one that I have been meaning to raise for a long time. One thing I think you missed though is the size of the environment. Everybody seems to be attacking your example of regional differences. You might take a look at different size of environment in the same location. For example, I go trout fishing in the sierra mountains here in california a lot. In the lakes you can find trout up to 10 lbs, but in the small creeks feeding the lakes you would be hard pressed to catch a trout bigger than 15 in. Are they stunted or otherwise not living a fulfilled life because they are in a small creek? I think not. they just grew to what there environment (size, food availability, etc) would allow. I speak of rainbow trout in my example.
 

DeputyChiefJR

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Could it also be that each species has a "healthy" introductory adult size...Could it be that they grow to fit their environment, but only after reaching a healthy "bare minimum" before stunting occurs? Thus someone with an oscar in a 280g might end up with a fish smaller than one that grew up in a 500 gal....
 

tai95

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I used to fish at a few farm ponds. Both had the same type of fish present Bass, Bluegill, Bullheads. The smaller of the two ponds the average bass would be around 8-10 inches. The other pond which was about twice the size the bass would 10-12 inches. Would this suggest that water volume does dictate size? It is a very intersting theroy though.
 
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