Food preferences were studied in 11 fish species in order to find out their potential as epiphyte and copepod controllers in Gracilaria cultures, The fish were exposed to mixtures of Gracilaria and Ulva with other epiphytes included, in the presence of copepods, and the intestinal content of the fish was determined. Aphanius dispar and Tilapia zillii (acclimated to seawater) emerged as potentially useful epiphyte controllers, and Aphanius dispar and Diplodus annularis were potential copepod controllers in Gracilaria cultures.