We examined the combined effects of fasting in freshwater and water temperature during the transition from freshwater to seawater on growth/metabolic parameters in juvenile chum salmon Oncorhynchus keta. Juveniles of 1 g in freshwater were first subjected to a 5-day fasting period at 10 or 5 °C, acclimated to either 10 or 5 °C seawater and fed ad libitum for 30 days. Control fish were transferred from 10 °C freshwater to 10 °C seawater and fed ad libitum throughout the experimental period. Serum insulin-like growth factor (IGF)-I was measured to evaluate growth status/potential and liver glycogen as an index of energy storage. Fasting in freshwater for 5 days negatively affected body size. Growth of juveniles kept at colder temperatures was retarded in seawater for at least 20 days, which may partly be explained by a lower feeding rate in cold seawater. Serum IGF-I levels were lower in fasted fish in freshwater at both temperatures and colder seawater had a negative effect on restoring serum IGF-I levels after refeeding for 20 days. Liver glycogen content was low in fish fasted in freshwater for 5 days. After refeeding in seawater for 10 days, liver glycogen content increased significantly in juveniles kept at colder temperatures. Colder water temperatures in both salinities positively affected glycogen content for 30 days after transfer to seawater, suggesting that juveniles allocated energy stores to the liver rather than growth under suboptimal feeding and temperature conditions. The findings of the present study suggested that relatively cold freshwater could negatively affect juvenile chum salmon growth soon after sea entry.

我们研究了从淡水到海水过渡期间禁食的淡水和水温对幼鲑鲑Oncorhynchus keta的生长/代谢参数的综合影响。首先将1 g淡水鱼的少年在10或5°C下禁食5天，使其适应10或5°C的海水，并随意喂食30天。在整个实验期间，将对照鱼从10°C的淡水转移到10°C的海水中，并随意喂食。测量血清胰岛素样生长因子（IGF）-I，以评估生长状态/潜力和肝糖原，作为能量存储的指标。在淡水中禁食5天会对身体尺寸造成负面影响。在海水中至少保持20天的时间，将温度较低的未成年人的生长延缓了，这在一定程度上可以归因于寒冷海水中较低的摄食率。在这两个温度下，淡水禁食鱼的血清IGF-I水平均较低，而较冷的海水在补充20天后对恢复血清IGF-I水平具有负面影响。在淡水中禁食5天的鱼肝糖原含量低。在海水中重新饲喂10天后，保持在较低温度下的未成年人的肝糖原含量显着增加。两种盐分中较冷的水温在转移到海水中后的30天内对糖原含量产生了积极影响，这表明幼鱼将能量存储分配给肝脏，而不是在最适度的摄食和温度条件下生长。本研究的发现表明，相对冷的淡水可能会在入海后不久对幼鲑的鲑鱼生长产生负面影响。两种盐分中较冷的水温在转移到海水中后的30天内对糖原含量产生了积极影响，这表明幼鱼将能量存储分配给肝脏，而不是在最适度的摄食和温度条件下生长。本研究的发现表明，相对冷的淡水可能会在入海后不久对幼鲑的鲑鱼生长产生负面影响。两种盐分中较冷的水温在转移到海水中后的30天内对糖原含量产生了积极影响，这表明幼鱼将能量存储分配给肝脏，而不是在最适度的摄食和温度条件下生长。本研究的发现表明，相对冷的淡水可能会在入海后不久对幼鲑的鲑鱼生长产生负面影响。