I like to start initially selling Fruitfish, Betas and Goldbulbs. Some fin types sell for a higher price than others. (But you have to keep an eye on the health of the Goldbulbs and sell them if it gets too low) and I always raise the prices a bit, and see what the crowd will pay for them.

There are fish that bring higher prices, but you have to figure out what they are. That's the fun part.

Trial and error is the best teacher as to what does and doesn't work well. and keep good records.
