Tropical Fish (item, not entity) can only be eaten when the player is hungry, and will not breed / tame cats or ocelots when they are right clicked. Neither cats nor ocelots will be attracted to the player when holding Tropical Fish.

-Right clicking an untamed cat with tropical fish does nothing - it acts as if the player were just holding any other item.

-Right clicking a tamed cat will make them sit / stand. 

-Right clicking a baby cat has the same effect. 

-Right clicking an untamed ocelot with tropical fish does nothing - it acts as if the player were just holding any other item.

(Cats and Ocelots are still attracted to the player when holding any Salmon or Cod, and both function as normal for breeding / taming/ attracting.)