What is the definition of a predatory fish?

Predatory fish belong to a wide range of different families and the anatomy differs greatly between the species. All predatory fish species have adapted to life as predators, but these adaptations can be very dissimilar. One of the most famous predatory fish species, the Piranha, is equipped with sharp teeth suitable for cutting loose pieces flesh and tearing them from the prey.


http://www.aquaticcommunity.com/predatory/

Predatory fish are fish that eat live animals as their food, usually other fish. They can be trained to accept dead food in captivity.

http://www.aquaticcommunity.com/predatory/

Many fish do not eat other fish.

Some fish are filter feeders, eating plankton. Others eat algae. Many eat insects at the surface, or fallen fruit.

"Parrotfish do not eat animals. Instead they eat small plant life, called algae, from rocks. Parrotfish get their name from the hard pointed mouths that looks like a parrot's beak. They use this special mouth as a tool to scrape the plants from the rocks."
http://www.fishid.com/learnctr/fisheat.htm

https://en.wikipedia.org/wiki/Fly_fishing

Then there are the bottom feeders.
https://en.wikipedia.org/wiki/Demersal_fish