Effect of prey items on the development of schooling behavior in chub mackerel Scomber japonicus in the laboratory

Chub mackerel Scomber japonicus can use both zooplankton and fish larvae as prey items depending on their dietary environment in their larval and early juvenile stages. Here, we compared the development of schooling behavior in chub mackerel fed either Artemia nauplii (plankton-fed group) or the yolk-sac larvae of red sea bream (fish-fed group). Video recording was conducted in rearing tanks followed by analysis of separation swimming index as a criterion of schooling behavior. As a result, early juvenile mackerel in the plankton-fed group did not show schooling behavior up to day 22 (at 25 mm standard length (SL)), whereas those in the fish-fed group completed schooling behavior on day 18 (at 19 mm SL). Lack of schooling behavior in the plankton-fed group may be attributed to the low level of highly unsaturated fatty acids, especially docosahexaenoic acid, in their diet, without which a deficiency in the development of the central nervous systems may have occurred. Alternatively, chub mackerel juveniles in the plankton-rich environment may have adapted the balance of feeding and antipredator performance and, thus, delayed the development of schooling.