I tamed this while on a pelagornis. Kill some fish, and put it on your hot bar. Land in the ocean on the pela. A ichthy or two might swim up to you. Feed fish meat when hungry. You got a ichthy! Also, you have to swim for them to follow. These are the pigeons of the sea (as well as tropical birds!) they will come and keep coming. It started with 1, then 2, then 4. Also pelas can only land on surface.