Black porgy (Acanthopagrus schlegeli), a euryhaline marine teleost, was used for the study of freshwater acclimation. This study examined for 1) optimum methods of freshwater acclimation, 2) blood physiological responses, prolactin (PRL) cDNA sequence ...

Black porgy (Acanthopagrus schlegeli), a euryhaline marine teleost, was used for the study of freshwater acclimation. This study examined for 1) optimum methods of freshwater acclimation, 2) blood physiological responses, prolactin (PRL) cDNA sequence and its mRNA expression during freshwater acclimation, 3) blood physiological responses and Na+/K+-ATPase activity of this fish treated with exogenous PRL during freshwater acclimation, 4) effects of oral administration of thyroid hormone on physiological activity and growth of this species reared in freshwater and seawater, and 5) stress responses to high water temperature on the fish reared in freshwater and seawater.
Methods of freshwater acclimation
Physiological responses of this fish were investigated during the acclimation from seawater to freshwater. In Exp.Ⅰ, the fish reared in the salinity of 35‰ was exposed step by step (2‰ per hour) to the salinity of 10‰ and this salinity remained for 72 hours. After that the salinity was again reduced step by step from 10‰ to 0‰ for 12 hours period (35-10-0). In Exp.Ⅱ, the salinity of fish rearing tank was abruptly reduced from 30‰ to 5‰and maintained this salinity for 24 hours. After that the salinity was abruptly reduced to 0‰ (30-5-0). In Exp.Ⅲ, the salinity of fish rearing tank was abruptly reduced from 35‰ to 0‰ (35-0). In Exp.Ⅳ, the fish already acclimated and reared in freshwater for 60 days was abruptly transferred to 35‰ seawater (0-35).
Plasma osmolality of the fish in Exp.Ⅰ (35-10-0) was significantly decreased at day-5 of experiment but recovered to the original level at day-10. In Exp.Ⅱ (30-5-0), osmolality of the fish was significantly decreased 3 hours after the experiment started but increased 6 hours after the start of experiment. Then, the osmolality was again decreased 36 hours after the start of experiment but began to recover after 48 hours. In Exp.Ⅲ (35-0), osmolality of the fish was continuously decreased until the end of experiment. However, osmolality of the fish in Exp.Ⅳ (0-35) changed insignificantly.
In Exp.Ⅰ (35-10-0), Plasma cortisol level of the fish was significantly increased (from 13.0～1.4 ng/mL to 29.5～14.8 ng/mL) at day-5 of the experiment but recovered to basal level (19.7～1.6 ng/mL) at day-10. The plasma cortisol level of the fish in Exp.Ⅱ (30-5-0) was significantly increased (from 34.1～7.7 ng/mL to 81.9～9.1 ng/mL) 24 hours after the start of experiment and recovered to the basal level (52.9～8.4 ng/mL) after 36 hours. Plasma cortisol level of the fish in Exp.Ⅲ (35-0) was significantly increased (from 9.8～4.5 ng/mL to 117.8～53.8 ng/mL) after 12 hours and recovered to the basal level (30.6～5.4 ng/mL) after 48 hours. However, cortisol level of the fish in Exp.Ⅳ (0-35) was not changed much. Glucose levels of the fish in the Exp.Ⅰ～Ⅲ showed a tendency of co-increase with cortisol levels but there were no significant differences in the Exp.Ⅳ. Hematocrit (Ht) of the fish in Exp.Ⅰ (35-10-0) showed no significant differences. In Exp.Ⅱ (30-5-0), Ht was increased 3 hours after the start of experiment but decreased after 6 hours, then recovered to basal level after 48 hours.
These results suggest that step-by-step adjustment of salinity was much better effect on osmoregulation and stress responses of this species during freshwater acclimation than abrupt adjustment.

1. 감성돔의 담수순화 방법:감성돔의 담수순화시 단계적인 염분변화는 급격한 염분변화에 비해 스트레스 및 삼투압조절 혼란이 적은 것으로 나타났다.
2. 감성돔의 담수순화시 혈액생리학적 반응 및 prolactin (PRL) mRNA의 발현: PRL이 삼투압조절 기관에 호르몬적 작 ...

1. 감성돔의 담수순화 방법:감성돔의 담수순화시 단계적인 염분변화는 급격한 염분변화에 비해 스트레스 및 삼투압조절 혼란이 적은 것으로 나타났다.
2. 감성돔의 담수순화시 혈액생리학적 반응 및 prolactin (PRL) mRNA의 발현: PRL이 삼투압조절 기관에 호르몬적 작용을 함으로써, 담수에서 감성돔의 고삼투압조절 능력이 향상되었음을 시사한다.
3. 외인성 prolactin (PRL) 처리 감성돔의 담수순화시 혈액생리학적 반응 및 Na+/K+-ATPase 활성: 외인성 PRL의 처리는 감성돔의 담수순화시 고삼투압조절 능력을 향상시키는 것으로 나타났다.
4. 담수 및 해수사육 감성돔의 생리활성 및 성장에 미치는 외인성 갑상선호르몬(T3)의 효과: 담수 및 해수사육 감성돔의 삼투압조절 향상 및 성장촉진을 위한 외인성 T3 공급 효과는 나타나지 않았다. 이러한 결과들은, 여러 생리적 기능의 활성화를 위한 갑상선호르몬의 적정 농도가 서로 다를 수 있음을 의미한다.
5. 담수 및 해수사육 감성돔의 고수온에 대한 스트레스 반응: 동일한 수준의 수온상승에 대하여 담수사육 감성돔이 해수사육 감성돔에 비해 더 많은 스트레스를 받고 있음을 시사한다.

본 연구는 해산 광염성 어종의 삼투압조절 생리에 대한 연구는 해수어류의 담수 및 기수양식 발전을 위해 많은 도움이 될 것으로 생각된다.