Many fish have the ability to change their growth trajectory according to the size of water.

If the water area is large, it will grow bigger and grow at a normal speed. If the waters are small, he will grow slowly, or not at all. In fact, it is obvious that fish tanks can't raise big fish. That's why we can't make good use of it.

Of course, I personally think that this is not the fish's active adjustment, but the size of the water determines the amount of food, so many fish compete for food, so it will not grow much.