Hirano T, Ogasawara T, Hasegawa S, Iwata M, Nagahama Y
Ocean Research Institute, University of Tokyo, Japan.
Gen Comp Endocrinol. 1990 May;78(2):254-62. doi: 10.1016/0016-6480(90)90012-b.
Returning chum salmon (Oncorhynchus keta) in northern Honshu Island, Japan, complete gonadal maturation while in the bay. Mature fish caught in the bay failed to survive in seawater for more than a week, whereas they adapted to fresh water efficiently. Mortality in seawater seems to be due primarily to an increased plasma osmolality. Maladaptation to seawater was more pronounced in the fish caught deep in the bay than those caught outside the bay, and also greater in females than in males. In close correlation with the increased plasma osmolality and electrolyte concentrations, plasma levels of cortisol and growth hormone increased in the fish kept in seawater. Cortisol and growth hormone may be secreted in response to the increased plasma osmolality and would not be the direct cause of the maladaptation to seawater. Plasma prolactin remained low in the seawater fish, indicating that the increased secretion of prolactin, a freshwater-adapting hormone, is not the cause of maladaptation to seawater either. On the other hand, when the fish caught in the river were kept in fresh water, an increase in plasma prolactin concentrations was seen, particularly in females, whereas no significant change was seen in plasma cortisol and growth hormone. Concentrations of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one in the female and of testosterone in both the male and female were extremely high in the bay fish and decreased slightly but significantly after 7 days in fresh water. The gonadal steroids may have inhibitory effects on osmoregulation in the mature salmon in seawater.
在日本本州岛北部洄游的大麻哈鱼（Oncorhynchus keta）在海湾中完成性腺成熟。在海湾捕获的成熟大麻哈鱼在海水中存活时间不超过一周，而它们能高效适应淡水。海水中的死亡似乎主要是由于血浆渗透压升高。与在海湾外捕获的大麻哈鱼相比，在海湾深处捕获的大麻哈鱼对海水的适应不良更为明显，并且雌性比雄性更严重。与血浆渗透压和电解质浓度升高密切相关，饲养在海水中的大麻哈鱼血浆中皮质醇和生长激素水平升高。皮质醇和生长激素可能是对血浆渗透压升高的反应而分泌的，并非海水适应不良的直接原因。海水饲养的大麻哈鱼血浆催乳素水平仍然较低，这表明催乳素（一种适应淡水的激素）分泌增加也不是海水适应不良的原因。另一方面，当在河流中捕获的大麻哈鱼饲养在淡水中时，血浆催乳素浓度会升高，尤其是雌性，而血浆皮质醇和生长激素没有明显变化。海湾中的大麻哈鱼雌性体内17α,20β-二羟基-4-孕烯-3-酮以及雄性和雌性体内睾酮的浓度极高，在淡水中饲养7天后略有下降但显著。性腺类固醇可能对海水中成熟大麻哈鱼的渗透压调节有抑制作用。
