Ion Regulatory Mechanisms of Chloride Cells in Chum Salmon

研究了鲑鱼（Oncorhynchus keta）鱼苗从淡水（FW）转移到海水（SW）后鳃氯细胞形态的变化。用Na^+， K^+-APTase α亚基特异性抗血清免疫细胞化学染色，在FW鱼苗的长丝上皮和板层上皮中均检测到氯细胞。SW转移不影响花丝中氯细胞的数量，但明显减少了片层氯细胞的数量。SW转移21 d后，纤维氯细胞的大小是FW鱼的1.8倍，而片层氯细胞的大小在整个实验过程中没有变化。转移到氯丝细胞SW后，免疫反应强度逐渐增强。这些结果表明，片层中的氯细胞可能是大马哈鱼鱼苗吸收离子的部位，而细丝中发育良好的氯细胞则负责大马哈鱼鱼苗的盐分泌。通过观察氯细胞分布和形态的变化，研究了成熟鱼在产卵迁移过程中的渗透调节能力。在日本本州岛北部的大口湾捕获的成熟大马哈鱼在SW的5天内死亡，血浆渗透压明显升高，而转移到FW的鱼则有效地维持了血浆渗透压。发育良好的氯化物细胞主要存在于海洋中捕获的未成熟鱼类的丝上皮中。然而，在海湾捕获的成熟鱼中，在板层上皮中也发现了额外的氯细胞。在SW和FW期，成熟鱼的长丝氯细胞数量明显减少，而片层氯细胞数量保持不变。这些结果表明，成熟大马哈鱼的低调节能力的丧失可能是由于纤维氯化物的减少，而片层氯化物细胞的出现可能是为即将到来的上游迁移做准备。少

Changes in gill chloride cell morphology were examined following transfer of chum salmon (Oncorhynchus keta) fry from fresh water (FW) to seawater (SW). Using immynocytochemical staining with an antiserum specific for the alpha-subunit of Na^+, K^+-APTase, chloride cells were detected in both filament and lamellar epithelia in FW fry. The number of chloride cells in the filament was not affected by SW transfer, whereas lamellar chloride cells were significantly decreased. The size of filament chloride cells was 1,8-fold larger than that of FW fish 21 days after SW transfer, whereas there was no change in the size of lamellar chloride cells throughout the experiment. The intensity of immunoreaction gradually increased after transfer to SW in filament chloride cells. These results suggest that chloride cells in the lamella may be the site of ion uptake in FW chum salmon fry and that the well-developed chloride cells in filament are responsible for salt secretion in SW.Osmoregulatory abil … More ity of mature chum during spawning migration was also examined by following the changes in the distribution and morphology of chloride cells. Mature chum salmon caught in Otsuchi Bay in northern Honshu Island, Japan, died within 5 days in SW in association with a marked increase in plasma osmolality, whereas the fish transferred to FW maintained plasma osmolality efficiently. Well-developed chloride cells were present mainly in the filament epitheliym of immature fish caught in the ocean. In mature fish caught in the bay, however, additional chloride cells were also found in the lamellar epithelium. The number of filament chloride cells decreased markedly in the mature fish both in SW and in FW,whereas the number of lamellar chloride cells was maintained. These results suggest that the loss of hypoosmoregulatory ability in mature chum salmon may be attributable to the decrease in filament chloride and that appearance of lamellar chloride cells may be preparatory to the forthcoming upstream migration. Less