EFFECTS OF CUMULATIVE LOADING LEVEL, AS FISH WEIGHT PER UNIT FLOW, ON WATER QUALITY AND GROWTH OF LAKE TROUT

Lake trout, Salvelinus namaycush, were cultured in a series of five rearing units (in triplicate). The fish removed available oxygen in each unit, from about 10.5 to 7.0 mg/L. Oxygen was replaced, through aeration, between rearing units. Effects of cumulative loading, as fish weight/flow rate, are described in terms of water quality and fish growth. In fish reared at the highest loading level, mean growth during the 2-month cumulative loading period was depressed by more than half. However, the growth rate progressively increased in those fish reared under high loading levels, indicating acclimation of the fish to high metabolite concentrations. After two months of series-reuse rearing, cumulative loading was removed through introduction of fresh water (noreuse) to each unit, and fish recovery was monitored. During recovery, mean growth of fish that had been reared under the highest cumulative loading level was equal to or greater than that of fish that had been reared under the low loading levels.