At the beginning of the game you are given a few fry and caviar, and already when they grow up, you try to cross them to get more species. At first do not do that. It is best to take away some of the most endless and expensive kinds of those that you have. Of course they can be mixed, but preferably not much. Since each time the mixing of the fish is becoming more often, die faster. To avoid this best fish fish mixed with each other.