COMPARISON OF WATER QUALITY, RAINBOW TROUT PRODUCTION, AND ECONOMICS IN OXYGENATED AND AERATED RACEWAYS
Clark, Michael Louis
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The effects of oxygenation and aeration on water quality, rainbow trout (Oncorhynchus mykiss) production, and economics were compared at the Wytheville State Fish Hatchery (WSFH) for 270 days. Mean dissolved oxygen (DO) concentrations and delta DO were significantly higher (P < 0.001) in the oxygenated raceways (9.5 and 2.75 mg/L, respectively) compared to aerated raceways (7.4 and 0.57 mg/L). Total settleable solids loads were significantly greater (P < 0.001) in aerated raceways (10.3 g/L/day) than in oxygenated raceways (8.8 g/L/day). Dissolved nitrogen (%), total gas pressure, and other water quality parameters (CO2, nitrite nitrogen, alkalinity, pH, and TAN) did not differ significantly between the treatments (P > 0.05). Raceway trout production (kg/day), trout growth rates (grams), feed conversion rate (FCR), and fish survival were not significantly different between treatments (P > 0.05). Blood hematocrit (Hct) and percent visceral mass were significantly elevated (P < 0.001) in oxygenated raceways compared to aerated raceways at 46 and 14.4% and 44 and 13%, respectively. Carrying capacity estimates derived from fish loading trials were significantly different (P < 0.001) at 3,355 and 2,217 kg/raceway in oxygenated and aerated raceways, respectively. Estimates of carrying capacity calculated using a fish loading (Ld) equation were also significantly different (P < 0.001) at 1,530 and 990 kg for oxygenated and aerated raceways, respectively. Oxygen injection increased the cost of production by $0.20/kg, however, net present value analysis (NPV) of oxygenated and aerated raceways over 5 years at a 10% discount rate yielded estimates of $50,666.51 and $32,742.15, respectively. Oxygen injection is an effective means of increasing DO concentrations, reducing effluent solids loading, and increasing raceway carrying capacity.
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