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USGS · 1014901

The loss of hyperosmoregulatory ability in migrating juvenile American shad, Alosa sapidissima

Joseph D. Zydlewski·S. D. McCormick
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Abstract

Investigations on juvenile American shad ( Alosa sapidissima ) revealed several physiological changes associated with downstream migration. Plasma chloride decreased 20% in wild juvenile shad during the autumn migration. Migrants had lower condition factor and hematocrit than non-migrant shad captured by beach seining. Gill Na + ,K + -ATPase activity of migrant shad was higher than non-migrant; a 2.5-fold increase was observed in 1993, while a 57% increase was observed in 1994. Similar changes were observed in laboratory studies of shad maintained in fresh water under simulated natural temperature and photoperiod. Plasma chloride dropped 68% and gill Na + ,K + -ATPase activity increased 3-fold over a 3-month period. Decreased plasma chloride was associated with increased mortality. Increases in gill Na + ,K + -ATPase activity decreases in plasma chloride and osmolality, and incidence of mortality were delayed and moderated, but not eliminated, in shad maintained at constant temperature (24°C). Shad did not survive in fresh water past December regardless of temperature regime. In seawater, all shad survived and showed no perturbation of plasma chloride at 24°C or simulated natural temperature (above 4°C). The decline in hyperosmoregulatory ability, as influenced by declining temperatures, may serve as a proximate cue for autumnal migration.

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Canadian Journal of Fisheries and Aquatic SciencesArticle

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BibTeXRIS

Joseph D. Zydlewski, S. D. McCormick. 1997. The loss of hyperosmoregulatory ability in migrating juvenile American shad, Alosa sapidissima. https://doi.org/10.1139/f97-144

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