i have 3 tankfulls of fish and not sure witch to sell any one know the least apealing fish to keep around i dont want to mess up my breeding variety

Definately sell any you can make again.
When in doubt, check the breeding charts in the guides section.

Marcey

but is there any that are just not usefull

I keep one example of as many fish as possible in one tank, and use the second for breeding as many examples of 'cash crop' fish (mainly magic ones) as possible in another.

They are all useful for breeding other fish, but there are many ways to find all of the species. It can be difficult to decide which ones to keep.

Some species can only come from eggs, so those are the ones that you really want to keep. They are also useful breeding stock for creating other species. Highlight the following for spoiler information: Silky Shark and Twin-Fin Spotanus are two very good fish to keep, since they cannot be bred from other fishies.

That depends on your goal for the game. Whether you want the magic fish only, or all the fish, or just a certain color. For instance, the orange fruitfish is pretty boring looking, and terribly easy to hatch; but if paired with a certain magic fish will yield a different magic fish.

Marcey