Abstract
Cyprinodon variegatus, a common resident of coastal Atlantic and Gulf of Mexico waters from Cape Cod, Massachusetts, to northern South America, lives in salinities ranging from freshwater (0 ppt) to at least 142 ppt. We studied the metabolic patterns of C. variegatus as influenced by rapid changes in ambient salinity (approximating tidal changes in native habitats) of individuals from a Florida Gulf of Mexico coastal salt marsh. Fish were acclimated to a series of salinities from 0 ppt to 60 ppt, with routine metabolic rates (RMR) determined at each acclimation salinity. The salinity was then changed (? 20 or 30 ppt) at a uniform rate over 6 h to simulate an extreme tidal change. Metabolic rates were then remeasured after the system attained a new steady state. Routine metabolic rate was unaffected by changes in salinity between 2 and 40 ppt. However, at salinities outside this range, RMR was affected by changes in ambient salinity. Individuals of C. variegatus responded to fluxes at salinity extremes by reducing metabolism and energy expenditures.
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