What you need to do is only breed common fish when you start... So breed the same fish or similar bodies like spotanus or fatfish. If you can breed magic fish 1 and 2 which should be able to be hatched from buying common and unusual eggs you can make a lot of money selling them. Only when you have enough money to research and obtain the environment research will you be able to breed other types of fishes. It will take time to make lots of money and obtain the research but once you have completed level 2 research which is the first step, you can start breeding new fishes that will live longer. Your goal is to make money to research all things, food, environment and advertising to level 3 which will allow fish to live, eat less and you will have more people in your store to buy the fish. Your other primary goal is to get another tank so you can breed more fish. My advice is to keep your important fish in one tank.. i.e. breeders and magic fish in one tank and pregnant fish in another and of course fish you don't need or cash cows in the sale tank.

cheers