Mass mortality associated with sudden sinking of larval barfin flounder, Verasper moseri
2003
Kayaba, T. (Hokkaido. Marine Cultivation Center, Shikabe (Japan)) | Sugimoto, T. | Matsuda, T.
Abstract: The present study was conducted to investigate the cause of mass mortality associated with sudden sinking of flexion larvae in barfin flounder, Verasper moseri. Observations on swimming behavior of larvae showed that most of the larvae suddenly sank from the upper layer to the bottom of the tank at 25 days of age, and that mass mortality occurred just after sinking. Coinciding with the sinking of larvae was an obvious increase in body density, especially in larvae from 24 to 28 days after hatching (dah) . In order to investigate the effects of turbulence on sudden sinking and mortality, 10 day-oId larvae were reared at various aeration levels, i.e., no aeration, gentle aeration and strong aeration. Larvae in both the no and gentle aeration groups sank suddenly at 24-25 dah and high mortality occurred. On the contrary, in the strong aeration groups, almost all larvae swam in the upper or middle layer throughout the experimental period. The survival rates at 36 dah were 74.3-89.0%, clearly superior to those in other experimental groups. These results suggest that sudden sinking of flexion larvae in this species is caused by a rapid increase in body density during a period of rapid ontogenetic change. It is likely that manipulating aeration to establish an vertical mixing is very successful for preventing flexion larvae from sinking, and hence, to avoid mass mortality.
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