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Responses of Young American Shad, Alosa sapidissima, to Low Temperatures
Author(s) -
Chittenden Mark E.
Publication year - 1972
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1972)101<680:royasa>2.0.co;2
Subject(s) - alosa , fishery , environmental science , biology , fish <actinopterygii> , fish migration
Responses of young American shad, Alosa sapidissima, to low temperatures in fresh water were studied in large aquaria with rapid temperature decreases (about 24 to 12 C) and with slow (1.9 to 0.5 C/day) decreases to 0.7 C in a tank with a temperature gradient. Rapid temperature decreases had no apparent effect. With slow decreases, the fish weakly avoided the cold end below 8 C and strongly below 5 C. Other sublethal effects included extremely sluggish movements below 6 C; cessation of feeding, frequent temporary equilibrium loss, wobbly swimming, and no response to hand movements below 4.4 C; and frequent collision with objects shortly before death. The lower thermal tolerance limit is about 2.2 C; prolonged exposure may increase this, because lethal temperatures depended on exposure time. Sublethal effects suggest that this species may not survive prolonged exposure to 4 to 6 C, particularly during autumn and early winter when the fish may not be acclimated. Temperature plays a multiple role in the diadromous movements of this species. It sets a limit on when the adults can enter and the young must leave fresh water. It masks the stimulus for upstream migration associated with gonadal development. Increases in temperature safely above the lower thermal limit release the expression of the gonadal stimulus. Temperature decreases in northerly rivers trigger a final exodus of young from fresh water. Avoidance and resistance lower the probability of mortality due to catastrophic temperature decreases. Cold water releases may adversely affect spawning and nursery areas below reservoirs.