They are a very important food source for many fish. Striped Bass and many other commercial fish feed on copepods as larvae, while other fish like bay anchovies and silversides remain plankton feeders their entire lives. Copepods occur in freshwater, estuarine, and marine ecosystems. Very small, newly hatched fish are not strong enough to swim substantially on their own, and are carried around the bay with the water currents. It is only for this early stage that fish are zooplankton.
Fish larvae feed mainly on other zooplankton, especially copepods.
Fish larvae are also very abundant in marshed and aquatic grass beds. The reason is that these locations provide the larvae with many places to hide from their predators. This is a drawing of what a striped bass looks like during the first 6 days of development. Cladocerans are crustaceans, but are in a different order than copepods. Anyone who has visited the Chesapeake in the summer knows just what these animals look like.