褐牙鲆幼鱼能量分配对限制溶解氧供应及恢复的响应

实验采用循环水养殖系统,通过水流量控制溶解氧供给,设计不同溶解氧供应和限制溶解氧供应及恢复两个实验来研究褐牙鲆(Paralichthys olivaceus)幼鱼生长及能量分配等指标的响应。在不同溶解氧供应实验中,溶解氧含量梯度设置为2.24 mg/L,3.14 mg/L,4.27 mg/L,5.38 mg/L,6.94 mg/L,实验结束时褐牙鲆幼鱼体重、日生长系数、摄食率、以湿重表示的饲料转化效率与溶解氧含量呈正相关(P0.05)。单尾鱼的摄食能随着溶解氧含量的下降而减少,生长能的比例在溶氧为5.38 mg/L时最高。排粪能的比例则随着溶解氧含量的下降而上升,排泄能比例随溶解氧含量下降也略有增加,代谢能的比例随着溶解氧含量的下降呈先下降后上升的趋势,在溶解氧含量为5.38 mg/L时最低(37.66%)。单位体重能量收支中,所有指标与溶解氧含量都有明显的正相关关系(P0.05),随着溶解氧含量的提高而显著提高。实验表明,低溶解氧含量下,褐牙鲆幼鱼通过减少能量供应降低摄食率和饲料转化效率,其生长受到抑制。在限制溶解氧供应及恢复实验中,经历10 d低溶解氧含量2 mg/L(S_2)和4 mg/L(S_4)胁迫的褐牙鲆幼鱼生长受到抑制,但在恢复正常溶解氧后10 d内体重即与对照组无显著差异(P0.05)。恢复期间褐牙鲆幼鱼的摄食率明显高于对照组(P0.05),饲料转化效率略高于对照组。恢复阶段不同处理在摄食能、生长能比例和呼吸能比例上没有显著差异(P0.05),但经历低溶解氧胁迫的处理摄食能和生长能比例略高于对照处理,而代谢耗能比例略低于对照处理。S2处理的排泄能比例显著低于其余2个处理(P0.05)。实验表明褐牙鲆幼鱼对短期低溶解氧含量有较强的适应能力,能够通过提高摄食率在较短的恢复期获得完全补偿生长。本研究揭示了褐牙鲆在低溶氧胁迫下的能量分配规律,为深入研究鱼类适应溶解氧波动环境的策略积累资料。

Responses of energy allocation to limited dissolved oxygen supply and recovery in juvenile brown flounder, Paralichthys olivaceus

The aim of this study was to investigate the growth and energy allocation responses of juvenile brown flounder, Paralichthys olivaceus, to a period of limited dissolved oxygen (DO) supply and recovery. This information is important to understand the adaptive strategy of brown flounder to fluctuations in DO. Juvenile brown flounder were kept in a recirculating system and the DO supply was limited by controlling the water velocity. Two experiments were designed to measure the growth responses and energy allocation. Across a wide range of DO (2.24-6.94 mg/L), the body weight, daily growth coefficient, feeding rate, and feed conversion efficiency (in wet weight) were positively related to DO (P<0.05). Individual energy ingestion decreased as the DO level decreased, and the highest percentages of growth energy were recorded at a DO level of 5.38 mg/L. Energy of feces increased and energy of excretion also increased slightly as the DO level decreased. The energy of metabolism decreased as the DO level decreased, then increased when the DO level fell below 5.38 mg/L. Energy allocation to metabolism was minimal at DO 5.38 mg/L (37.66%). For energy allocation per 1 g body weight, all parameters were positively related to DO and increased as the DO level increased. The growth of juvenile brown flounder was depressed during 10 d in low-DO conditions2 mg/L(S₂) and 4 mg/L (S₄)]. However, when the fish kept in low-DO conditions were transferred to control conditions, their body weight recovered to that of control fish within 10 d. Compared with the fish in the control, those kept in low-DO conditions showed a higher feeding rate during the recovery period and slightly higher feed conversion efficiency. There were no significant differences among the different treatments in energy ingestion, growth energy, and energy of metabolism during the recovery period (P>0.05). However, compared with control fish, the fish kept in low-DO conditions showed slightly higher energy ingestion and growth energy, and slightly lower energy of metabolism. Energy of excretion was lower in the S₂ group than in the other groups. Low DO levels decreased the feeding rate and feed conversion efficiency of juvenile brown flounder by depressing the energy supply, leading to depressed growth. These results show that juvenile brown flounder can adapt well to a short period of low DO, and completely compensate for the growth depression in a short period of recovery by improving their feeding rate.