Comparison of behavioural development between Japanese flounder (Paralichthys olivaceus) and spotted halibut (Verasper variegatus) during early life stages

Abstract

Summary Behavioural development was compared between two flatfish species (Japanese flounder and spotted halibut) from hatching to settlement (juvenile stage) in order to speculate on the ecology of their early life stages and to provide fundamental knowledge for improving seedling production techniques for stock enhancement. Fish were cultured under identical rearing conditions (500-L tank maintained at 17.8 ± 0.4°C, 34 ppt, 10L : 14D light regime and an initial stocking density of 20 larvae L−1). Behavioural observations were conducted at about 4-day intervals from hatching to the juvenile stage. Fish were sampled randomly from the rearing tank, and one fish was transferred into a 250-ml observation container. Behaviour was video-recorded for 5 min without food and for an additional 5 min with live feed (rotifer or Artemia). All behavioural data were sorted according to eight developmental stages and compared among developmental stages and between species. The average standard length of the spotted halibut was significantly greater than that of the Japanese flounder in all developmental stages, while the development of Japanese flounder was faster than that of the spotted halibut. For Japanese flounder, feeding, swimming and Ohm-posture (typical shivering behaviour observed during early life stages in flatfishes) frequency were highest before metamorphosis (mean ± SD; 1.0 ± 2.0 attacks min−1, 24.0 ± 9.6 actions min−1, 1.1 ± 1.1 counts min−1, respectively). Spotted halibut expressed feeding behaviour frequently from the beginning of metamorphosis (3.6 ± 5.2 attacks min−1), had relatively low swimming activity during all developmental stages, and showed a peak of Ohm-posture frequency during the flexion stage (2.6 ± 1.0 counts min−1).