Food selection by young larval gulf menhaden (Brevoortia patronus)

Abstract

Food selection by young larvae of the gulf menhaden (Brevoortia patronus) was studied in the laboratory at Beaufort, North Carolina (USA) in 1982 and 1983; this species is especially interesting, since the larvae began feeding on phytoplankton as well as microzooplankton. When dinoflagellates (Prorocentrum micans), tintinnids (Favella sp.), and N1 nauplii of a copepod (Acartia tonsa) were presented to laboratory-reared, larval menhaden (3.9 to 4.2 mm notochord length), the fish larvae ate dinoflagellates and tintinnids, but not copepod nauplii. Larvae showed significant (P<0.001) selection for the tintinnids. Given the same mixture of food items, larger larvae (6.4 mm notochord length) ate copepod nauplii as well as the other food organisms. These feeding responses are consistent with larval feeding in the northern Gulf of Mexico, where gulf menhaden larvae between 3 and 5 mm in notochord length frequently ate large numbers of dinoflagellates (mostly P. micans and P. compressum) and tintinnids (mostly Favella sp.), but did not eat copepod nauplii. As larvae grew, copepod nauplii and other food organisms became important, while dinoflagellates and tintinnids became relatively less important in the diet. Since the tintinnids and nauplii used in the laboratory feeding experiments were similar in size as well as carbon and nitrogen contents, the feeding selectivity and dietary ontogeny that we observed were likely due to a combination of prey capturability and larval fish maturation and learning.