Feeding Habits of Pacific Cod Larvae and Juveniles in Mutsu Bay, Japan

Abstract

The diets and prey widths of Pacific cod (Gadus macrocephalus) larvae and juveniles were examined in Mutsu Bay. In early March, 11 yolk-sac larvae were caught in midwater ofthe bay mouth. Five of 11 larvae captured had not opened their mouths, and the remaining six had notfed. Post-larvae ≤ 7mm in total length (TL) fed on copepod nauplii, particularly Pseudocalanus nauplii. Prey items of post-larvae >7mm TL were chiefly crustacean eggs, and Pseudocalanus spp. copepodites and adults. From April to June, the main food organisms of cod juveniles were calanoid copepods, and changed from Pseudocalanus spp. to Calanus pacificus, Acartia clausi, and Centropages abdominalis. In addition, cod juveniles opportunistically fed on large-sized food organisms, namely, reptant megalopae, planktonic gastropods, and natant zoeae. In July, cod juveniles mainly fed on benthic prey items, such as gammarid amphipods and fish. It seems probable that these large-sized food organisms play an important role as alternative prey for cod juveniles when they change their mainfood from calanoid copepods to benthic prey items.