Diel and ontogenetic changes in larval body density related to swim bladder volume were investigated in Paci¢c blue¢n tuna, Thunnus orientalis, to determine the causality of larval mortality^adhesion to the water surface and contact with the tank bottom during seedling production. The density of larvae with de£ated swim bladders increased with total length and days post hatch. Diel density change was observed after day 2 post hatch; owing to daytime de-£ation and night-time in£ation of the swim bladder, the density was relatively higher during the daytime. Increased swim bladder volumes clearly reduced larval density during the night-time after day 9 post hatch. However, the density of larvae with in£ated swim bladders was greater than rearing water density (Dr40.0099). The small density di¡erence between larvae and rearing water (Dr 5 0.0022 À 0.0100) until day 4 post hatch may have caused larval mortality by adhesion to the water surface because larvae can be easily transported to the water surface by aeration-driven upwelling in rearing tanks. Density increased noticeably from day 5 to day 9 post hatch. The increased density di¡erence (Dr 5 0.0065 À0.0209) in larvae and rearing water possibly induced mortality by contact with the tank bottom because larvae sink particularly during the night-time on ceasing swimming.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.