There is a way to get a good deal of money when starting out without cheating (sorta)

Get yourself an orange fruitfish, orange stickfish, and a silky spotanus. With these 3 hardy fish, you can breed the less hardy Pink Leaffish (Orange fruitfish and silky spotanus) And then using the leaffish and orange stickfish, breed was groupers. I breed 12 groupers, put them all in the sell tank, use all 3 drops of the growth hormone to get them fully grown, then sell them before they die. $95 per grouper Makes you a lot of money and quite quickly. Just don't leave them for much, they die quick :/