Individual variability of self-feeding activity in group-reared barfin flounder

Abstract

Individual variability of self-feeding activity in group-reared barfin flounder Verasper moseri was examined under natural photoperiod and water temperature. A self-feeder with a string trigger and a switch sensor, and a charge-coupled device (CCD) camera were placed in each of six tanks. Activation of the self-feeder resulted in delivery of three pellets (approximately 0.2 g in total), and each activation was recorded by an event logger. Self-feeding behavior of tagged fish (three or five fish per tank) was recorded continuously on video for 24 h once a week for 4–12 weeks. In all tanks, the fish learned self-feeding within 2 days, were mostly nocturnal feeders, and immediately consumed all the pellets provided by the feeder. All the fish gained body weight during the experimental period. In three tanks, significant differences were observed in the number of feeder activations per 24 h among individuals, i.e., one fish mainly triggered the switch. In contrast, in the other three tanks, no significant differences were observed in the number of feeder activations per 24 h among individuals. These results indicate that barfin flounder attain appropriate growth by using the self-feeding systems independently of whether or not individual differences in the number of self-feeding activities were observed.