Assuming it is a fish, wait until a visual particle effect appears on you and/or on the fish. That specific particle effect is associated with one of the three angling commands: Fish Reel, Fish Juke, Fish Troll. You need to deduce through trial and error which particle effect is associated with which angling command. Each specific type of fish has its own three particle effect / angling ability associations, but they are always consistent for the same species of fish. (For example, for Perch, the three associations are purple smoke erupting from your headand lightning above the fish, stack of flowers rising from the fish, and colorful yellow and purple sparkles on both the fish and your pole, corresponding to Reel, Juke, and Troll.)