Empirical verification of feeding selectivity of larval and juvenile pelagic fishes using in-situ zooplankton communities

Abstract

Abstract A significant number of field researches have described the diet of larvae and juveniles of commercially important pelagic fish species. However, due to possible biases related to net sampling, including i) bycatch of target fish with prey that are not sympatrically distributed, ii) overestimation of prey that are not easily digested in the gut of target fish, and iii) regurgitation and excretion of gut contents from target fish during sampling, it is uncertain whether the results obtained from those studies truly represent the situation of live fish in the sea. Therefore, we conducted a laboratory experiment minimizing the above uncertainties in the field sampling. Hatchery-reared juvenile chub mackerel (Scomber japonicus) and larval Japanese anchovy (Engraulis japonicus) were used as experimental fish, which was fed with wild-caught zooplankton assemblages collected around Hakatajima Island in Setouchi inland sea (133.10°E, 34.20°N). The relationships between fish size and prey number in the gut, and the selectivity on each prey organism were determined. As a result, in both species, prey number and size increased with body size, and the fish showed strong selectivity for crustaceans including copepodites and adults of copepods. These results substantially support the conclusions of previous field studies.