Almost exclusively live fish; wide variety of species taken, both marine and fresh-water. Size of prey also varies greatly, but generally 8-14 inches (20 - 36 cm) in length. Because Ospreys can dive only about 0.5 - 1.0 m deep, they are restricted to surface-schooling fish, or to those in shallow water.
In very general terms, comparisons of the ecology of fish taken by Ospreys over a broad expanse of their range showed that benthic-feeding fish (taken only in shallow waters) are the easiest to catch and that in the limnetic-zone piscivorous fish are harder to catch than non-piscivorous fish (Swenson 1979). Benthic feeders may have their attention focused down on food, rather than up where the Ospreys are, and limnetic piscivores are faster than their nonfish-eating relatives.
Very few data on diet from Central and South America. In the southern Florida keys, spring/summer: Speckled trout (Cynoscion nebulosus) (64%); striped mullet (Mugil cephalus) (27); sea catfish (Galeichthys felis) (Szaro 1978) -- probably typical for Ospreys in the Caribbean as these species are widespread there.
In coastal mangroves of Santos and Cubatão, Brazil, key species in the diet of wintering Ospreys: mullets (Mugil spp.) and pompanos (Diapterus rhombeus), representing 77% and 18%, respectively, of 90 prey items recorded (Silva e Silva and Olmos 2002).
Other anecdotal observations from the Neotropics and Caribbean/Gulf waters: Ospreys wintering in the Sea of Cortez leave piles of skulls of coronet fish (Fistularia sp.) under feeding perches on Cardon cacti, and on the upper Texas coast, wintering Osprey (common) take many saltwater catfish (Gafftops sp.; R. A. Behrstock pers. comm.). E. Malaga (pers. comm.) observed Osprey taking Mugil cephalus from lagoons in Mejia along southwest coast of Peru. Some 20 observations of Ospreys taking red piranha (Pygocentrus caribe) in the Venezuelan llanos (C. Sharpe pers. comm.).