초록
숭어, Mugil cephalus의 염분별 삼투조절 능력을 알아보기 위하여, 전장 $13.6{\pm}0.2cm$, 체중 $20.0{\pm}0.5g$ 크기의 재료를 해수 (SW)에 담수를 첨가하여 만든 $0\%SW\~100\%SW$에 수용한 다음, 60일간 사육하면서 염분별 혈액의 이온 농도와 삼투질 농도 변화를 조사하고, 아가미와 염세포의 조직학적 변화 및 근육의 수분함량을 비교하였다. $0\%SW\~25\%SW$에서 숭어 혈장의 $Na^+$와 $K^+$ 농도는 실험개시후 8일째부터 안정되었다. $0\%SW$에서의 혈장 $Cl^-$ 농도는 실험개시후 0.5일째 가장 낮았으며 2일 이후부터 안정되었다. 실험종료시에 있어서 숭어 혈장의 삼투질 농도는 저염분 일수록 낮아지는 경향을 보여, $100\%SW$부터 $0\%SW$까지 각각 340, 334, 322 및 316 mOsm/kg 수준으로 안정됨으로써, 저염분에서는 저삼투 조절을 하는 것으로 나타났다. 이와 함께 hematocrit도 염분이 낮아짐에 따라 감소하는 경향이었다. $0\%SW\~50\%SW$에 10일째 노출된 숭어의 아가미에서는 2차새변이 손상되었으며, 특히 $0\%SW$에서는 2차새변의 박리, 유착 및 괴사 등이 관찰되었다. 그러나 손상된 아가미는 이후부터 회복되기 시작하여 사육 15일째에 정상적인 조직상을 나타냈다. 염분에 따른 각 염분구별 어체 근육의 수분함량에는 차이가 없었다.
In order to investigate the osmoregulation capability of grey mullet, Mugil cephalus with the different salinities, juvenile fish $(13.6{\pm}0.2\;TL)$ stocked in seawater (SW) were abruptly transferred to each experimental group $0\%SW(0\%_{\circ}),\;25\%SW(7.7\%_{\circ}),\;50\%SW(16.1\%_{\circ})\;and \;100\%SW(32.8\%_{\circ})$ and reared for 60 days. Blood samples were taken by the time schedule after the transfer. Plasma $Na^{+},\;K^{+},\;Cl^{-}$ and osmolality, muscle water content, and the electron microscopical observations of chloride cells were analyzed and made by the time schedule. In $100\%SW$, the maintainable levels of plasma $Na^{+},\;K^{+},\;Cl^{-}$ and osmolality were $167.1{\pm}7.7mM/l,\;9.1{\pm}2.1mM/l,\;137.8{\pm}5.6mM/l\;and\;351{\pm}18\;mOsm/kg$, respectively. These values were significantly changed at $6h\~1\;day$ after the beginning of the experiment with four different salinities. Fish from $0\%\;and\;25\%SW$ had lower osmolalities than those of fish from $50\%\;and\;100\%SW$, and showed the hyposmotic regulation pattern. At the end of the experiment (60 days after transfer), however, no significant difference was found in the concentrations of plasma $Na^{+},\;K^{+}\;and\;Cl^{-}$ among four experimental groups. Hematocrit was increased with salinity (P<0.01). After 10 days, fish from $0\%\;and\;25\%SW$ showed the hypertrophy, fusion and edema of epithelial layer in gill lamella. However, at the 15th day, epithelial layer in gill lamella was back to the normal status. On gill of fish from $0\%SW$, one apical pit held two or three chloride cells in common. Muscle water content was subsequently regulated to near the normal levels within 4 days, and there was no significant difference among four different salinities at the end of the experiment.
(Department of Aquaculture, Pukyong National University)
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