Effect of ambient salinity on ionic and osmotic regulation of eggs, larvae, and alevins of rainbow trout (Salmo gairdneri)

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Abstract
The osmotic concentration of the perivitelline fluid in eggs of rainbow trout (S. gairdneri) was lower in eggs maintained in distilled water than in eggs maintained in dilute artificial sea water (11.permill. and 13.permill.). Water content of eggs, larvae and alevins in distilled water was significantly higher than in comparable developmental stages in dilute sea water. Similarly, differences were found in the tissue Na+, K+ and Na+:K+ ratios of eggs, larvae and alevins reared in the different ambient salinities. The early developmental stages of rainbow trout possess a limited capacity for osmotic or ionic regulation. Larvae appear to regulate tissue Na+ content by increasing the Na+ concentration of the perivitelline space, and alevins tolerate an increase in tissue K+ content and a small decrease in tissue water content.