The following chart will tell you what you can expect when you breed any two fish.

http://spreadsheets.google.com/ccc?key=p_i-N4Gj-HYFPRlnmyEKvdQ

Before you use this chart you have to know that each time you breed two fins together (e.g. silky and twin-fin) will always give you the same result (e.g. golden) no matter what the body type is. The same goes for the body - each time you breed two body types together (e.g. spotanus and bananafish) you will always get the same body type as a result (e.g. quicksilver) no matter what the fin type is.

On this spreadsheet Sheet 1 lists the results for all fin types. Sheet 2 lists the results for all body types. Sheet 3 lists the default prices for fin/body combinations, as well as naming which fish are magic. Using these three charts you should be able to easily make all the magic fish without having to hunt and peck.

Early in the game you use the price chart to create a more expensive fish that will survive in your tank (probably aim for around $20-30) and breed it until you have enough money to upgrade your fish environment all the way.

Currently I am working on finding all the default prices for every fin/body combination as well.