Physiological Consequences of Overwintering in Streams: The Cost of Acclimitization?

Abstract

Proximate body composition and hematological parameters of wild brook (Salvelinus fontinalis) and brown trout (Salmo trutta) from five sites were monitored over three winters. For both species, and for immature and mature fish, lipid levels were lowest (and water content highest) in winter. Lipid levels were most rapidly depleted (to between 2 and 4% wet weight) in early winter (November–December). Brown trout and immature brook trout appeared to suffer a second period of depletion in late winter (February–March) in contrast with spent brook trout. Protein and ash components were relatively stable between dates. Serum protein levels varied greatly but generally indicated a decline in early winter from high summer (August) values prior to increasing in May. Such trends were most obvious during the winter of 1983–84, the harshest of the three winters of study. In the winter, serum glucose concentrations peaked in November. These physiological relationships corroborate earlier findings that early winter is a stressful period of acclimatization to rapidly changing environmental conditions. Even the relatively stable discharge and temperature regimens of spring-fed tributaries are insufficient to offset the effects of early winter.