First, you need to hatch some common and uncommon eggs until you hatch both a Crimson Goldshark (Uncommon) and a Magic Fish of Nutrition (Common). Breeding these two fish which are very easily obtainable will get you the Golden Guppy of Isola. The Golden Guppy of Isola can be sold for over $200, making it an ungodly fast way of making money if you mass-breed them. Being able to breeze through the game and obtain rare fish VERY quickly.