Ontogenetic and temporal changes in the diet of the Chilean silverside Odontesthes regia (Atherinidae) in Southern Chile

The Chilean silverside Odontesthes regia (Humboldt, 1821) is a common fish in the littoral of Southern South America mainly observed in estuaries, spawning areas of the species. Information on its diet in these environments is scarce, especially for juveniles. We studied the ontogenetic changes in diet of the Chilean silverside in the estuary of the Rio Valdivia (Southern Chile). Three size classes were considered in the analyses according to sexual maturity: small (< 50 mm), medium (50-140 mm) and large (> 140 mm). The analysis of the stomach contents was related to the food offer in the four seasons of the year. The 287 stomachs analysed contained a wide variety of food items, including 35 invertebrate taxa as well as plant debris, unidentified detritus and fish scales. Small-sized individuals fed mostly on zooplankton, particularly on copepods and ostracods; medium-sized fish consumed a combination of benthonic invertebrates and zooplankton while large individuals fed mainly on benthonic crustaceans. Although temporal differences were observed in the diet of the silversides, the ontogenetic organization (small, medium and large sizes) was maintained. Based on the results of different stomach contents for different size classes, O. regia should be classified as a selective omnivorous predator.