When a young fish has used up all of the nutrition from its yolk-sac, it has to start consuming zooplankton.

Aquatic invertebrates slightly larger than zooplankton are also an important source of food for small fish. These invertebrates comprise the diet for many species of fish even as adults. Such invertebrate-consuming fish species include all small-sized species, such as small cyprinids like the common roach. Some larger species of fish also eat invertebrates. For example, the common bream likes to feed on insect larvae it finds near the bottom of the water. 


The common roach.

Many species fish eat other fish. They are considered predators. The pike is an excellent example of a predator fish. It has a large mouth, sharp teeth, and it is lightning-quick. Perch become predators when they grow over 15 cm long. 

Salmon and trout are likewise predators. They become predators once they move away from their birth locations to dwell in the sea or in lakes. Once there, they begin hunting for smaller fishes, such as herring.


The pike is a predator.