Ok, I'll tell ya ...
The answer is Nekton ... Nekton can be contrasted with plankton ...
Essentially, Nekton are "free swimmers" such as fish, the exemplar of the type. Many are not aware that Plankton is not a biological classification per se, as it includes larval animal forms, as well as plants.
I have always been pleased to think of the term "nekton" as a justification for Melville's insistence, in Moby Dick, that the whale is a fish. That is, he is using "fish" for "nekton", and this makes the whole thing rhetorically consistent.
I’m thinkin’ napalm. Tried and tested.
Gee one more useless fact learned on fr.