| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1992: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1991: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
Teleosts from the different salinity are able to maintain their blood osmolality at about 1/3 of that of seawater. Osmoregulation has been suggested under control of the endocrine system such as prolactin, cortisol and growth hormorn. In the salmonid fish, plasma hormone levels have been measured with a specific radioimmunoassay, and the changes in their receptors are studied. Ultra-structure of the osmoregulatory organs like gill, kidney and intestine has also been reported. The present study, however, is to approach the various mode of fish osmoregulation, especially from the view point of the whole organisms level. Following results are obtained from the present study ; 1. Handling stress has made significant influence on the plasma electrolyte levels in the rainbow trout. Special attention should be needed when studied aquatic animals. 2. In the guppy, histological observations showed activation of the chloride cells, when transferred to hypertonic environment. No change was observ
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ed in the intestine or kidney. Chloridecell might function earlier than other osmoreguratory organs begin to work. On the other hand, 3. Neontetra originated from the Amazon survived in deionized water, although they are unable to adapt to the environment with increased salinity. Chloride cells of the neontetra showed no change. There may be correlation between the activation of the chloride cells and survival in the environment with increased salinity. 4. In the goldfish, acute increase in plasma osmolality was seen during transfer to seawater. When transferred back to fresh water after short-term dipping to seawater, however, the plasma osmolality was soon adjusted at normal level. From the result maximum level of the plasma osmolality was assumed to which the goldfish tolerate. It is suggested that in the hypertonic environment, salt permeability to the body surface of goldfish is much higher than that of the typical euryhaline teleosts such as salmon. This may be limiting factor which make a difference in the adaptability of the teleosts to the environment with increased salinity. Less
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