What is the difference between a fish and a lobster?

Not only is a lobster bigger than a cray fish but it stays in salt water other than fresh water

in the group, all the fish are of the same species = use "fish" in the group, the fishes are of different species = use "fishes"

Lobster tail is just the tail. Lobster is the whole thing.

well iwould liek to say what type of question is that a human is a mamal a fish is an aquatic creature .........fish breath through gills what do we as humans breath through, can human's live...

I think you mean 'mammals'. And the answer is a lot, considering most mammal ancestors evolved from the first fish. For instance, mammals are often covered in hair, have four limbs and produce milk...