| Abstrakt: |
Snake River cutthroat trout (Oncorhynchus clarki) of the Bar BC strain were reared at four densities in triplicate for 18 weeks. Supplemental oxygen was required in the rearing units holding the three highest densities to maintain adequate dissolved oxygen (DO) levels of 6–7 ppm (61–71% of saturation) after the last feeding in the afternoon. Density indices (lb!ft3 per inch of fish length) achieved for each treatment averaged 0.48, 1.40, 2.12, and 2.30, and fish density averaged 3.43, 10.56, 15.56, and 15.42 lb/ft3, respectively, at the conclusion of the study. Survival, weight gain, feed conversion, and fish health were adversely effected by increased density; however, dorsal and pectoral fin condition, total length, length variation, and water quality were not adversely effected. Neither un-ionized ammonia (maximum, 0.0051 ppm) nor total carbon dioxide (maximum, 24.2 ppm, pH 7.5) concentrations reached detrimental levels. Over a 24-h period at the end of the study, daily DO consumption averaged 274 g/kg of feed (SD, 32 g/kg) when the fish were fed at 1.3% of body weight. During this period, maximum DO consumption occurred while fish were being fed (0700 to 1500 hours), and average DO consumption was 149 mg/kg of fish body weight per hour (SD, 17 mg/kg). Overall, the fish averaged 40.1 g (SD, 17.1 g) and consumed DO at a rate of 167 mg/kg body weight per hour (SD, 15.7 mg/kg). There were no differences in the rate of DO consumption due to fish density. Fish densities averaging 15.56 Ib/ft3 were achieved in this study. This is four to five times greater than densities achieved without supplemental oxygen, but fish performance was affected. [ABSTRACT FROM PUBLISHER] |
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