Hatchery-reared, 0 + age smallmouth bass (Micropterus dolomieui) of 55-107 mm total length were wintered from Sept. 1975-May 1976. Temperature regimes were modeled on those of the natural environment and final temperatures were 2, 4 and 6.degree. C. Final wintering temperature did not noticeably influence mortality rates. Long fish survived the period of low temperature better than did shorter ones. Body ratios of dry weight/wet weight, lipid weight/dry weight and ignitable weight/dry weight all decreased during wintering. There may be critical percentages of dry weight/wet weight and ignitable weight/dry weight below which these fish will die.