Ok I'm going to keep this short, simple and straight to the point. When you first start off with this game do not, and I repeat do not cross breed any of your fish with different species, do not do that until you have gained enough research skills to keep exotic/mutant fish in your tanks. They're fragile and will die at a very young age, meaning you will be wasting a lot of time and tank space trying to keep ill fry.

The smart thing to do at the start is to breed your high earning fish with the same EXACT species till you have gained a huge amount of money to max out your research skills. By doing that it will allow you to start experimenting with insane cross breeding.

Oh and another tip, don’t be afraid to use your Sale Tank as a breeding tank to hold your fry. Be sure to place growing fish in there as well, the baby fish will not be sold so you don’t have anything to worry about.