순치 기간에 따른 육봉형 산천어(Oncorhynchus masou masou)의 해수 적응능력

Abstract

The seawater adaptability of land-locked masu salmon Oncorhynchus masou masou via acclimation was examined for aquaculture purposes. The survival, blood chemistry, and histological changes of masu salmon (150 g) were measured after 7-, 15-, and 30-day acclimation periods. After a total of 60 days in seawater cultures that incorporated the various acclimation periods, survival was 83.5, 87.2, and 91.0% for the 7-, 15-, and 30-day periods, respectively; thus, survival increased with longer periods of acclimation. Feeding efficiencies were 32.1, 52.0, and 40.6% for the 7-, 15-, and 30-day periods, and specific growth rates were 0.14, 0.26, and 0.23%, respectively. Generally, masu salmon appeared to exhibit better growth performance after an acclimation period of 15 days. Cortisol concentrations [mean <TEX>${\pm}$</TEX> SD] for 7, 15, and 30 days of acclimation were <TEX>$21.0{\pm}6.5$</TEX>, <TEX>$17.8{\pm}4.8$</TEX>, and <TEX>$21.2{\pm}5.4\;{\mu}g/dl$</TEX>, with the lowest values occurring with 15 days of acclimation. Osmolarities were <TEX>$359.2{\pm}26.1$</TEX>, <TEX>$350.4{\pm}29.2$</TEX>, and <TEX>$354.6{\pm}29.3$</TEX> mOsm/kg, and glucose concentrations were <TEX>$60.7{\pm}20.7$</TEX>, <TEX>$72.9{\pm}17.3$</TEX>, and <TEX>$76.6{\pm}14.1$</TEX> mg/dl for the 7-, 15-, and 30-day acclimation periods, respectively (P < 0.05). The histological study revealed that both gills and both kidneys of the masu salmon exhibited middle- to end-stage and middle-stage lesions in the 7- and 15-day groups, respectively, whereas these organs only had early-stage lesions in the 30-day group in the final experiment. Therefore, the seawater acclimation of masu salmon should involve more than 30 days in seawater.