Mortality of reared flounder (Paralichthys olivaceus) juveniles released in Shijiki bay [Japan].
1992
Sudo H. | Goto T. | Ikemoto R. | Tomiyama M. | Azeta M.
Experimental releases of 37,000 (33.7mm TL) and 24,600 (81.2mm TL) reared flounder juveniles were carried out in Shijiki Bay in 1985 and 1986, respectively, to elucidate the process and mechanism of their mortality. Total numbers of recaptured fish were 577 and 450 in 1985 and 1986, respectively, and most of them were caught within 10 days after release. Decrease rates of released fish were therefore high in both years (17.6%.day-1 in 1985 and 45.1%.day-1 in 1986). However, the process of their decrease and adaptation was different. In 1985: (1) the decrease rate of small fish (TL<35mm) was higher than that of large ones; (2) albinic fish decreased more rapidly than normal ones; (3) feeding incidence was low. In 1986: (1) there was no difference in decrease rate between small (TL<75mm) and large fish; (2) decrease patterns were similar between albinic and normal fish; and (3) feeding incidence was high. These results suggest that the most significant cause of decrease of released fish was predation in 1985 and dispersal in 1986, because it is easy for predators to catch and handle small and starving fish and to detect albinic fish.
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