Abstract
We investigated the optimal conditions for behavioral observation of Pacific bluefin tuna Thunnus orientalis and observed behavioral development with special reference to aggressive behavior. Different colored tanks and light intensities were tested against survival in 10-h period. While low survivals (0-10%) were observed in dark colored containers and high light intensity (>900 lx), clear tanks and medium light intensity (600 lx) had high survival (60-80%). With latter conditions, preliminary observations on the behavioral development of swimming behavior (swimming speed) and aggressive behavior (chase frequency) were performed at different developmental stages; mouth opening (2 days after hatching, DAH), pre-flexion (3 DAH), flexion (13 DAH), post-flexion (18 DAH) and juvenile (19 DAH) using different batches. Mouth opening was at 2 DAH (standard length, SL, mean±SD, 2.9±0.1 mm) and juveniles first appeared at 19 DAH (SL 6.3 mm). Frequency of chase behavior in relation to feeding was observed for 36 DAH juveniles. Swimming speed maintained constant values from hatch until the flexion stage (3.7±3.9-9.5±14.3 mm/s). Aggressive fish first appeared on 16 DAH (SL 5.4±0.9 mm, flexion stage) and frequency of chase behavior did not change until the juvenile stage. Chase behavior was more frequent when juveniles were starved.
