Development of swimming speed and schoolingbehavior of juvenile white rockfish (Sebastes cheni) in relation to ambient light intensity


Nakano, Hikaru, Koji Hirakawa, and Jun Shoji
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To clarify the ontogenetic changes in antipredator behavior of juvenile white rockfish (Sebastes cheni), effects of light intensity (0.1, 1, 10, 100, 1000, and 10,000 lx) and body size (23.4, 30.3, 41.1, 49.4 and 58.6 mm in total length [TL]) on swimming (cruising [swimming] speed [CS] and burst [swimming] speed [BS]) and schooling behavior (nearest neighbor distance [NND] and separation angle [SA]) were examined under laboratory conditions. The CS was higher under higher light intensities for all length classes. The BS increased with increases in fish body size at the highest light intensity although there was no significant effect of body size at the lowest light intensity. The NND was largest for the smallest fish-size class at all light intensities. The effects of light intensity and fish body size on SA were not significant. Schooling behavior of the juvenile white rockfish was determined to begin to develop at body sizes >30 mm TL. In this study, we found the ability of juvenile white rockfish to avoid predation through schooling behavior to be minimal in comparison with other species because the instinct appears to not be well developed during the early postsettlement period (20–30 mm TL).