EFFECTS OF ELEVATED SUMMER TEMPERATURES AND REDUCED PH ON METABOLISM AND GROWTH OF JUVENILE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) ON UNLIMITED RATION

Juvenile trout (Oncorhynchus mykiss) were exposed to a simulated globa l warming - acidic water scenario over a 90-day summer period (control temperature range 13-24 degrees C). The addition of 2 degrees C to th e fluctuating summer cycle of inshore Lake Ontario and H2SO4 to synthe tic soft water resulted in four treatments: control, acidification of control, simulated global warming alone, and global warming plus acidi fication. The twice-daily feeding regime raised metabolic rates to sim ilar to 75% of Mo-2(max). Large increases (from 4.5 to 11.5%) in whole -body lipid, smaller increases (from 12.0 to 15.5%) in protein, and co mpensating decreases in water content (from 77 to 71%) occurred in all treatments over time. The addition of 2 degrees C resulted in depress ed appetites and growth, particularly after the period of peak tempera ture (days 60-90; 26 degrees C). Metabolic rate and nitrogenous waste excretion were also depressed. Overall, exposure to low pH resulted in increased appetites and growth, the increase of 2 degrees C reduced g ross energy intake and increased fecal energy losses, and exposure to low pH resulted in increased energy intake and gain and better convers ion efficiency. The lack of ionoregulatory disturbance in trout chroni cally exposed to pH 5.2 suggested that dietary NaCl may have compensat ed for branchial ion losses.