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The seawater tolerance of juvenile fish from an anadromous and a landlocked population of Arctic char (Salvelinus alpinus), reared in freshwater under a constant light regime, was compared by making repeated seawater challenge tests from one summer to the next. Fish from the landlocked population had higher mortality rates and higher blood plasma Na+ concentrations after transfer to seawater than those from the anadromous population. The gill Na-K-ATPase activity of the landlocked fish was lower than that of the anadromous fish. For both populations, the smallest fish showed the lowest seawater tolerance, but hypoosmoregulatory ability was independent of fish size for fish larger than about 60 g. By June of the second summer, fish from the anadromous, but not those from the landlocked population, developed seawater tolerance 10 d after transfer to seawater. This increase in hypoosmoregulatory ability was accompanied by a doubling of the gill Na-K-ATPase activity.

STAURNES, M, LYSFJORD, G., and BERG, 0 . K. 1992. Parr -smolt transformation of a nonanadromous population of Atlantic salmon (Salmo salar) in Norway. Can. J. Zool. 70: [197][198][199]. Morphological and physiological indices of parr-smolt transformation of fish from anadromous and nonanadromous hatchery-reared populations of Atlantic salmon (Salmo salur) were compared. Both anadromous and nonanadromous Atlantic salmon showed a complete smolt colouration and had a similar high gill Naf ,K+-ATPase activity (significantly (P < 0.05) different from that of parr), indicating both morphological and physiological aspects of parr-smolt transformation. The evolutionary stability of the parr-smolt transformation of nonanadromous Atlantic salmon is discussed. STAURNES, M, LYSFJORD, G., et BERG, 0 . K. 1992. Parr-smolt transformation of a nonanadromous population of Atlantic salmon (Salmo salar) in Norway. Can. J. Zool. 70 : 197 -199. Les signes morphologiques et physiologiques de la transformation de tacons en saumonneaux ont Cte compares chez des Saumons atlantiques (Salmo salar) anadromes et des saumons non anadromes Clevks en pisciculture. Chez les poissons des deux types, la coloration de saummonneau Ctait complkte et l'activite de la Nat ,K + -ATPase (significativement (P < 0,05) differente de celle des tacons) dans les branchies etait semblable, ce qui indique que la transformation morphologique et la transformation physiologiques s'etaient produites chez les deux types de saumons. La stabilite evolutive de la transformation de tacon en saumonneau chez les Saumons atlantiques non anadromes fait I'objet d'une discussion.[Traduit par la redaction]

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