Leedsichthys was a giant fish that would have dwarfed every other animal in the Jurassic sea, but it was a gentle giant that lived on the tiny shrimps, jellyfish and small fish that make up plankton. It would have swum slowly through the upper waters of the ocean, taking mouthfuls of plankton-rich water and sieving them through the giant mesh-plates at the back of its mouth. Its feeding habits were similar to the modern blue whale, which also survives on nothing but plankton.
Leedsichthys appears in Jurassic Park: Builder. Once you have purchased the Leedsichthys into your Jurassic Park, it will begin at evolution 1 as a baby. As you feed it with crustaceans the fish will grow. It evolves at level 5 into an adult form or evolution 1. Once this evolution reaches its maximum at level 10 it will be able to evolve into evolution #2 through researching.
Once it evolves into its evolution #2 in the research center, it will become a baby again. Upon doing this you must feed it once again until level 15, where it will evolve into its adult form. After reaching level 20 you will be able to research and evolve the fish again at level 20 where it will evolve into its last form.
After level 20 it will become a baby again but in an entirely new form with a new coloring and much more earning compared to the previous. It will evolve in level #3 at level 25.