I think it depends on the style and approach of the game (which you can decide )
Do you want it to be realistic, then scale everything like/ similar to reality. Or if you go for fun, play a bit and "highlight" things with bigger scale as you like.
If it was more cartoony or pixelated style, would it look weird if a bass was the size of a boat? Or could it possibly make sense that underwater the fish look bigger and then once they are reeled up they become smaller?