In laboratory experiments young-of-the-year green sunfish, Lepomis cyanellus, largemouth bass, Micropterus salmoides, brook trout, Salvelinus fontinalis, and yellow perch, Perca flavescens, were held for 4 mo under simulated winter conditions (2–4 °C; photoperiod of 9 h light: 15 h dark) in solutions of various osmotic strengths, from 90% distilled water to 1.0% NaCl. Mortality in three of five experiments often was greater in salt solutions, indicating that NaCl did not increase survival. Survival was greater for larger yellow perch than smaller but was not related to size in the other species. Hematocrit was depressed below control levels in all solutions at the end of experiments. The fish generally were able to regulate plasma osmotic concentration in all solutions except the highest NaCl concentrations, where plasma osmolality was often significantly higher than in the control at the end of experiments. Plasma Na+ and Cl− typically decreased and then recovered at low temperatures. Presence of Na+ and Cl− in the external medium tended to alleviate their loss from plasma. Changes in plasma Na+ and Cl− were not related to mortality in hypoionic solutions but usually did correspond to changes in plasma osmolality. Fat content of survivors declined and water content increased for all species, but the losses and gains were not related to osmolality of solutions. Low fat content probably was not a cause of death.Key words: Mortality, electrolyte regulation, osmolality, hematocrit, fat depletion, winter conditions, green sunfish, largemouth bass, brook trout, yellow perch, sodium, chloride
Recruitment dynamics of non-native largemouth bass within the Sacramento-San Joaquin Delta
