Swanson C
Department of Biology, University of California, Los Angeles, CA 90095, USA.
J Exp Biol. 1998 Dec;201 (Pt 24):3355-66. doi: 10.1242/jeb.201.24.3355.
The euryhaline milkfish (Chanos chanos) is an excellent subject for studies of the physiological and behavioral processes involved in salinity adaptation. In this study, energy partitioning for metabolism, activity and growth, maximal activity performance and blood osmotic concentrations were assessed at two activity levels in juvenile milkfish fed equal rations and maintained at a relatively constant temperature (262 C) and at salinities (15, 35 and 55 ?) that represented a wide range of osmoregulatory challenges. Changes in the measured parameters were not consistently related to the magnitude of the trans-integumentary osmotic gradients. Routine oxygen consumption rates were high in 35 ? salinity (mean 1 s.e.m. 1678 mg O2 kg-1 h-1) and comparably low in 15 and 55 ? salinity (1336 and 1273 mg O2 kg-1 h-1, respectively). Routine activity levels (relative swimming velocity) were highest in 35 ? salinity (0. 960.04 L s-1), where L is standard length, intermediate in 15 ? salinity (0.770.03 L s-1) and lowest in 55 ? salinity (0.670.03 L s-1). Growth was significantly higher in 55 ? salinity (3.40.2 % increase in wet body mass per day) than in 35 ? salinity (2.40.2 % increase per day) and intermediate in 15 ? salinity (2.90.5 % increase per day). Maximum swimming velocities decreased with increases in salinity, from 9.90.7 L s-1 in 15 ? salinity to 6.60. 5 L s-1 in 55 ? salinity. Sustained swimming activity above routine levels for 2 h resulted in an increase in blood osmotic concentrations in milkfish in 55 ? salinity, but osmoregulation was re-established during the second 2 h of activity. Thus, patterns of variation in metabolic rate and growth were largely parallel to variations in routine activity although, comparing 15 and 55 ? salinity, elevated maintenance costs for osmoregulation at the high salinity were detectable. Reduced osmoregulatory abilities and reductions in maximal swimming performance suggest that high salinity may constrain activity. The results demonstrate that investigations of salinity adaptation in euryhaline fishes should take into account the interactive effects of salinity on physiology and behavior.
广盐性虱目鱼（Chanos chanos）是研究盐度适应过程中生理和行为过程的绝佳对象。在本研究中，对投喂等量饲料、维持在相对恒定温度（26±2℃）以及代表广泛渗透调节挑战的盐度（15、35和55‰）下的幼体虱目鱼，在两种活动水平下评估了代谢、活动和生长的能量分配、最大活动性能及血液渗透浓度。所测参数的变化与经皮渗透梯度的大小并非始终相关。在35‰盐度下常规耗氧率较高（平均值±标准误为1678毫克O₂·千克⁻¹·小时⁻¹），在15‰和55‰盐度下相对较低（分别为1336和1273毫克O₂·千克⁻¹·小时⁻¹）。常规活动水平（相对游泳速度）在35‰盐度下最高（0.96±0.04体长·秒⁻¹，其中体长为标准长度），在15‰盐度下居中（0.77±0.03体长·秒⁻¹），在55‰盐度下最低（0.67±0.03体长·秒⁻¹）。在55‰盐度下生长显著高于35‰盐度（湿体重每天增加3.4±0.2%），在35‰盐度下为（每天增加2.4±0.2%），在15‰盐度下居中（每天增加2.9±0.5%）。最大游泳速度随盐度增加而降低，从15‰盐度下的9.9±0.7体长·秒⁻¹降至55‰盐度下的6.6±0.5体长·秒⁻¹。在55‰盐度下，持续游泳活动高于常规水平2小时会导致虱目鱼血液渗透浓度增加，但在活动的第二个2小时内渗透调节得以重新建立。因此，代谢率和生长的变化模式在很大程度上与常规活动的变化平行，不过，比较15‰和55‰盐度时，可检测到高盐度下渗透调节的维持成本升高。渗透调节能力降低和最大游泳性能下降表明高盐度可能限制活动。结果表明，对广盐性鱼类盐度适应的研究应考虑盐度对生理和行为的交互作用。
