Evaluation of some physiological parameters as predictive indices of smoltification [of coho salmon]
1981
Folmar, L.C. (North-West and Alaska Fisheries Research Center, Seattle (USA)) | Dickhoff, W.W.
During smoltification of coho salmon (Oncorhynchus kisutch) in freshwater (April-May), dramatic increases in both plasma T(,4) and gill Na('+)-K('+) ATPase activities were observed and found to be significantly related. Plasma T(,3) levels increased in some groups during this period and, overall, were significantly correlated with both plasma T(,4) and gill Na('+)-K('+) ATPase. A significant decrease in plasma Na('+) and Cl('-) concentrations was observed in some groups. Transfer to seawater resulted in significant increases in gill Na('+)-K('+) ATPase activity during the first 8 d of seawater residence. In contrast, plasma T(,4) and T(,3) concentrations showed variable response. Plasma concentrations of the thyroid hormones were significantly correlated with one another, but unrelated to ATPase activities. The lack of a significant relationship between plasma T(,4) concentrations and gill Na('+)-K('+) ATPase in seawater suggests that they may be freshwater developmental phenomena which prepare the fish for seawater entry rather than serving as regulatory mechanisms after seawater entry. All hatchery groups showed rapid increases in both plasma Na('+) and Cl('-) during the first or second day of residence in seawater. All physiological measurements obtained in both fresh water and seawater were compared with the number of surviving and smolted fish after 6 months in seawater. Only one relationship, a component of the plasma T(,4) curve from fish in fresh water and percentage survival, was found to be significant. The usefulness of this comparison in predicting hatchery release dates is discussed.
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