What do small wild fish eat?

It depends on where they live. Fish of the smaller variety often eat plant and animal matter that lies on the ocean floor (i.e. a decaying piece of kelp or fish). Some small fish will eat tiny organisms that populate the watery environment around them; there are many types of crustaceons and other animals that may be almost too small to see with the naked eye, but make a perfect snack for a small fish. In freshwater areas, small fish will also prey on insects that land on the water's surface or the larvae of insects that spend their larval stage underwater (like mosquitos). In fact, there is a species of tiny fish related to guppies that people actually purchase to live in their backyard ponds or other standing pools of water. The fish prey on the water-bound mosquito larvae, thus drastically reducing or eliminating a mosquito population that once relied on the pool of water to reproduce. With the onset of West Nile virus in the United States, sales of this little fish have skyrocketed, as West Nile virus is often transmitted by mosquitoes.