|MadSci Network: General Biology|
I've heard that one myself- that the size of a fish depends on the size of the aquarium it's in. For instance- if you put a goldfish in a bowl, it will stay goldfish size, but if you put them into a pond, they'll grow much larger (I've been told that that is what koi are).
That is mostly what we nowadays call an "old spouse's tale", but there is a grain of truth to it. Here's why- the container doesn't limit the size of the fish (in other words, the fish doesn't "know" how big a tank it's in and stop growing when it reaches some size that it knows to be "right"). Think of a goldfish in a bowl- it will grow, so long as you feed it. Eventually, that goldfish will get big enough that the tank is too small for it- it will have trouble swimming, it will therefore have a harder time eating, and it will be producing a lot more waste that will foul the water. This leads to an unhappy, stressed goldfish, one that will be more susceptible to disease, and it will eventually die. So I suppose what you could say is that the size of a fish's environment can limit its size, but not necessarily determine it. For a good article on this topic, check out this article on fish and aquarium size from the Greater Seattle Aquarium Society.
In the case of fish in a more natural setting, the size of the body of water that they live in generally isn't very closely related to growth. In that case, the productivity of the ecosystems there(which will determine how much prey is available to fish) is generally more closely tied to growth.
Hope that helps!
Rob Campbell, MAD Scientist
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