| Budget Amount *help |
¥2,500,000 (Direct Cost: ¥2,500,000)
Fiscal Year 1997: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 1996: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
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
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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
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