Abstract

The effects of sudden changes of water temperature (WT) on the stress response and physiological change of the cultured olive flounder in large (FL) and small (FS) size, and fat cod (FC) were examined by manipulating WT (2 types) in a flow through seawater culture system with 6 tanks (water vol. 270 L/tank). The WT was decreased from $20^{\circ}C$ to $10^{\circ}C$ within 5 hours ($2^{\circ}C/hour$) and maintained at $10^{\circ}C$ for 21 hours (Exp. I), and it was raised from $20^{\circ}C$ to $30^{\circ}C$ within 5 hours and maintained at $30^{\circ}C$ for 21 hours (Exp.II). In Exp. I, the levels of blood hematocrit at 5 hours ($10^{\circ}C$) in FS was significantly decreased from $13.5\pm2.0\%\;to\;11.3\pm2.3\%$, but FC at 2.5 hours ($15^{\circ}C$) ($19.0\pm0.3\%\;to\;23.2\pm3.8\%$) was increased, The blood hemoglobin concentration of all fish in Exp, II was significantly increased until 8 hours after raising WT from $20^{\circ}C$ to $30^{\circ}C$. In Exp. I and II , the levels of plasma cortisol in FL, FS and FC was changed from $5.2\pm8.5ng/mL,\;4.4\pm4.5ng/mL\;and\;2.7\pm0.4ng/mL$, respectively, before sudden drop and rise of WT. The levels of plasma cortisol of in FL ($164.0\pm53.1ng/mL$) and FC ($207.9\pm25.4ng/mL$) were significantly increased by the lowering WT sharply during whole experiment. The FL ($12.6\pm2.0ng/mL$) and FS ($4.0\pm3.9ng/mL$) showed no significant differences in cortisol level according to sudden rise of WT (5 hours). But it in FC ($44.7\pm18.2ng/mL$) was increased. In Exp. I, the plasma glucose levels of all fish groups were decreased after 5 hours ($10^{\circ}C$), The plasma lactic acid concentration of FL and FS showed no significant differences until 5 hours after raising WT from $20^{\circ}C$ to $30^{\circ}C$, But it in FC was significantly increased with WT raise.

1회성의 수온급변 실험으로서 크게 2가지 형태의 수온변화 조건을 주었다: $20^{\circ}C$로부터 시간당 $2^{\circ}C$씩 수온을 떨어뜨려 $10^{\circ}C$까지(소요시간 5시간) 낮춘 다음, 21시간 유지한 것 (Exp.I)과 $20^{\circ}C$로부터 시간당 $2^{\circ}C$씩 수온을 상승시켜 $30^{\circ}C$까지 (소요시간 5시간)올린 다음, 21시간 유지한 것 (Exp. II). 수온을 $20^{\circ}C$로부터 $10^{\circ}C$로 급격하게 낮춘 실험에서 실험어의 Ht는 넙치대 $11.6\pm0.2\sim15.5\pm0.1\%$, 넙치소 $9.0\pm0.4\sim13.5\pm2.0\%$, 쥐노래미 $18.3\pm3.6\sim23.2\pm3.8\%$의 범위로서 쥐노래미가 넙치에 비하여 높은 값을 나타냈다. 코티졸 농도는 넙치소에서 유의한 변화를 보이지 않은 반면, 넙치대와 쥐노래미에서 실험개시시에 각각 $5.2\pm8.5ng/mL,\;2.7\pm0.4ng/mL$였던 것이 $10^{\circ}C$ 하강시에 각각 $164.0\pm53.1ng/mL,\;207.9\pm25.4ng/mL$로 크게 높아졌다. 젖산은 넙치대에서는 실험개시시에 비해 차이를 보이지 않았으나, 넙치소와 쥐노래미에서 개시시 보다 낮아져 글루코스 농도의 변화와 비슷하였다. 수온을 $20^{\circ}C$로부터 $30^{\circ}C$로 급격하게 높인 Exp. II에서 실험어의 Hb 변화는 모든 어종에서 수온급상승에 따라 약간 높아지는 경향을 보이다가 실험개시시의 수준으로 회복되었다. 쥐노래미에서는 수온급변에 따라 MCV는 상승하는 반면, MCHC는 하강하였다. 넙치대·소의 코티졸 농도는 Exp. I의 결과와 같이 큰 변화를 나타내지 않았다. 그러나 쥐노래미에서는 실험개시시의 $2.7\pm0.2ng/mL$로부터 $44.7\pm9.1ng/mL$로 높아졌다. 글루코스 농도는 모든 어종에서 실험개시시 보다 높아져 Exp.Ⅰ결과와는 반대되는 경향을 나타냈다.

Keywords

• Paralichthys olivaceus;
• Hexagrammos otakii;
• Sudden water temperature change;
• Stress;
• Physiology;
• Cortisol