The presence of abundant natural food in the water partly ensures a good growth of the fish even without supplemental feeding. During the fry-to-fingerling stage, Nile tilapia feed on plankton - tiny free-floating plants (phytoplankton) and animals (zooplankton) some of which are visible only under a microscope. Water rich in plankton is brownish, bluish-green or grass-green in color. Grayish or murky water indicates a low natural food productivity.

Tilapia cage farming. (1985, September 30). Bulletin Today, p. 30.