Effects of hypoxia on growth and metabolism of juvenile turbot

The effects of hypoxia on growth, feed efficiency, nitrogen excretion, oxyg en consumption and metabolism of juvenile turbot (120 g) were studied in a 45-day experiment carried out in sea water at 17.0 +/- 0.5 degrees C and 34 .5 ppt salinity. Fish were fed to satiation at O-2-concentrations of 3.5 +/ - 0.3, 5.0 +/- 0.3 mg l(-1) (hypoxia) and 7.2 +/- 0.3 mg l(-1) (normoxia). Both feed intake (FI) and growth were significantly lower under hypoxia tha n under normoxia, with no significant differences being observed between 3. 5 and 5.0 mg O-2 l(-1). During the first 2 weeks of the experiment, FI was halved under hypoxic conditions, and there were large differences among tre atments in feed conversion ratio (FCR), i.e., it was 3.2, 1.5, and 0.9 in t urbot exposed to 3.5, 5.0, and 7.2 mg O-2 l(-1), respectively. Thereafter, FCR was not significantly affected by O-2-concentration. Nitrogen excretion and oxygen consumption of feeding fish were significantly higher under nor moxia than under hypoxia, but following 7 days of feed deprivation oxygen c onsumption was similar under normoxia and hypoxia. Plasma osmolarity, ionic balance, and acid-base status were not affected by the two hypoxic conditi ons tested. Overall, our results indicate that turbot have some capacity to adapt to relatively low ambient O-2-concentrations. (C) 2000 Elsevier Scie nce B.V. All rights reserved.