THE EFFECT OF DISSOLVED-OXYGEN ON THE GROWTH OF YOUNG-OF-THE-YEAR WINTER FLOUNDER, PSEUDOPLEURONECTES-AMERICANUS

The effects of constant and diurnally fluctuating levels of dissolved oxygen on the growth of young-of-the-year winter flounder, Pseudopleuronectes americanus, were examined under controlled laboratory conditions. Fish were exposed for either 10 or 11 weeks to constant levels of 6.7 (high) and 2.2 (low) mg l-1, and a diurnal fluctuation, ranging from 2.5 to 6.4 mg O2 l-1. Growth rates, calculated for both standard length and weight, for fish exposed to low and diurnally fluctuating levels were significantly reduced (p < 0.001) as compared to those for fish exposed to the high level. Growth rates of fish exposed to the high level were over twice those of fish held under low oxygen conditions. Under fluctuating conditions, fish grew at intermediate rates. Following these exposures, all fish were subsequently held at 7.2 mg O2 l-1 for five weeks. Growth rates increased over two and a half times for fish previously exposed to the low oxygen level and were significantly (p < 0.001) higher than for the other two groups.