The best way to keep baby fish alive is to research your environment. Once you reach level three you will not see your babies dying anymore. As far as your $$$ question goes... to avoid creating a spolier i'll give you this advice. The first time you sell your fish double the orginal price. Once your in the store watch the customers recations to the prices. If you see red unhappy faces in the bubbles and your fish are not selling decrease the price by $5. If they like the price and the fish sell quickly increase the price $5. Keep this up until your fish sell at a resonable rate and you have a mixture of responses from the customers.