Zhang Li, Wang Wen-Xiong
Department of Biology, The Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong, China.
Aquat Toxicol. 2007 Aug 30;84(2):173-81. doi: 10.1016/j.aquatox.2007.03.027. Epub 2007 Jun 26.
Metal uptake and toxicity in marine fish are usually much lower than those in freshwater fish, but the underlying mechanisms remain unclear. In this study, we investigated Cd and Zn uptake by the euryhaline black sea bream (Acanthopagrus schlegeli) over a salinity range from 0 to 35 psu. Cd and Zn uptake increased as salinity decreased. The gills were the most sensitive organs in response to salinity change, and played a more important role in Cd and Zn uptake at a lower salinity. Cd and Zn uptake in the viscera contributed to 34-36% of the overall accumulation at full salinity (35 psu), but decreased to 13-16% in freshwater despite the increase of uptake rate. Water permeability, drinking, and major ion uptake (Ca) in the fish at different salinities were also concurrently examined. The overall water uptake was comparable, whereas the drinking rate decreased at lowered salinities. In contrast, the Ca uptake increased significantly with decreasing salinity. The responses of Cd and Zn uptake to salinity challenge were correlated with the Ca uptake, suggesting that they may be taken up through the Ca uptake pathway. At a constant salinity, Cd and Zn uptake increased with reducing Ca concentration, indicating the competitive effect of Ca on metal uptake. Ca channel blockers (verapamil and lanthanum) significantly reduced the uptake of Cd, Zn, and Ca when the fish were acclimated in freshwater, but had no impact on their uptake in marine water. Furthermore, the chloride cell number in the gills could not explain the lower Cd and Zn uptake in seawater. Our results indicated that both ambient physicochemical factors and the physiological responses of fish resulted in difference of metal uptake in marine and freshwater environments.
海洋鱼类对金属的摄取和毒性通常远低于淡水鱼，但其潜在机制尚不清楚。在本研究中，我们调查了广盐性黑鲷（Acanthopagrus schlegeli）在盐度范围从0至35 psu时对镉和锌的摄取情况。镉和锌的摄取量随着盐度降低而增加。鳃是对盐度变化最敏感的器官，并且在低盐度时对镉和锌的摄取中发挥更重要的作用。在内脏中，镉和锌的摄取量在盐度为35 psu时占总积累量的34 - 36%，但在淡水中尽管摄取速率增加，却降至13 - 16%。我们还同时检测了不同盐度下鱼类的水通透性、饮水量以及主要离子（钙）的摄取情况。总体吸水量相当，而饮水量在低盐度时下降。相反，钙摄取量随着盐度降低而显著增加。镉和锌摄取对盐度挑战的反应与钙摄取相关，表明它们可能通过钙摄取途径被吸收。在恒定盐度下，镉和锌的摄取量随着钙浓度降低而增加，表明钙对金属摄取具有竞争作用。当鱼在淡水中适应时，钙通道阻滞剂（维拉帕米和镧）显著降低了镉、锌和钙的摄取，但对它们在海水中的摄取没有影响。此外，鳃中氯细胞数量无法解释海水中较低的镉和锌摄取量。我们的结果表明，环境物理化学因素和鱼类的生理反应都导致了海洋和淡水环境中金属摄取的差异。
