THE IMPACT OF CONSTANT AND FLUCTUATING OXYGEN CONCENTRATIONS AND 2 WATER-CONSUMPTION RATES ON POST-SMOLT ATLANTIC SALMON PRODUCTION PARAMETERS

The effects of two water consumption rates and oxygen fluctuation regi mes on various post-smolt Atlantic salmon (0.6-1.4 kg) production para meters were studied during a 126 day period. Fish, reared in a land-ba sed single-pass system were kept in six circular 25-m(3) outdoor tanks at 8.0+/-0.5 degrees C, and divided into three groups (A, B and C) su bjected to various water consumption rates and dissolved oxygen concen tration (DO) fluctuations: (A) low water consumption (0.20 l kg(-1) fi sh min(-1)) and no DO fluctuations (constant 7.3 mg l(-1)); (B) low wa ter consumption (0.20 l kg(-1) fish min(-1)) and large DO fluctuations (4-13 mg l(-1)); C. high water consumption (0.40 l kg(-1) fish min(-1 )) and medium DO fluctuations (5-10 mg l(-1)). Two replicate trials we re conducted within each experimental group. An automatic regulation s ystem added oxygen gas into the inlet water to group A tank in order t o maintain constant DO concentrations in the outlet water Oxygen gas w as added into the inlet water to group B and C tanks at constant rates throughout the day, leading to fluctuating DO concentrations in the o utlet wafer caused by metabolic rate fluctuations of the fish. No sign ificant difference in growth and FCR was evident between the three exp erimental groups during the study period. The results show that DO flu ctuations within 4-13 mg l(-1) (mean 8.5 mg l(-1)) did not have a nega tive effect on fish growth, mortality and FCR, compared with fish rear ed at a constant DO concentration (7.3 mg l(-1)). Water consumption ra tes that were reduced to 0.20 l kg(-1) fish min(-1), did not influence growth and FCR in salmon, compared with higher rates (0.40 l kg(-1) f ish min(-1)). The economical impact of the of automatically, as oppose d to manually, operated oxygen regulation systems, are discussed.