Therefore using 32 Bit textures wouldnt increase the detail of each fish
I never said that increasing the bit depth of the textures would increase the "detail" of the fish or the background. If Jim wants to add more detail to the fish, he can do so by modifying the 3D model of each fish or he can give the illusion of more detail by using bump mapping. As for the background, well.....3D is all I have to say.
An increase in bit depth means an increase in the number of colors available, this usually results in a more color rich presentation. There are other items that factor into the end result as well, which flipper was kind enough to point out.