Response of channel×blue hybrid catfish to chronic diurnal hypoxia

Performance traits and metabolic responses of the channel×blue hybrid catfish (Ictalurus punctatus female×I. furcatus male) in response to chronic diurnal hypoxia were evaluated in this 197-d study. Sixteen 0.1-ha earthen ponds were stocked with 15,169 hybrid catfish/ha (47g/fish) and managed to maintain the minimum dissolved oxygen concentration greater than 12%, 24%, 36%, or 48% of saturation. Growth and yield of channel×blue hybrid catfish were significantly related to minimum nightly dissolved oxygen concentration. The cumulative effect of nocturnal dissolved oxygen concentration and the duration of exposure to hypoxia (termed dissolved oxygen-minutes) proved to be a better independent variable for regression analysis than minimum nightly dissolved oxygen concentration. Gross and net yield and mean individual weight increased curvilinearly as dissolved oxygen-minutes increased. Chronic nightly hypoxia affected daily feed consumption and channel×blue hybrid catfish in the higher dissolved oxygen treatments grew faster because they consumed a greater percentage of their body weight at each feeding. Feed consumption increased linearly in response to dissolved oxygen-minutes during the peak production period (June–August), but curvilinearly over the entire study. Body compositional indices largely were unaffected by chronic nightly hypoxia. Lipid was the primary depot affected by hypoxia and lipid indices increased with increasing dissolved oxygen concentration and with increasing total feed fed. Citrate synthase activity was 14.6% higher in the highest compared to the lowest dissolved oxygen treatment and a strong inverse relationship between citrate synthase activity and fish body mass was observed in the highest dissolved oxygen concentration treatment. Results of this study suggest that pond dissolved oxygen concentration should be maintained at 48% saturation during the peak production period (water temperatures above 25C) and at 36% saturation during the rest of the growing season. ► Nightly dissolved oxygen affects channel x blue hybrid catfish productivity. ► Duration of exposure proposed as new independent variable. ► Chronic nightly hypoxia affected daily feed consumption. ► Lipid was the primary depot affected by hypoxia. ► Citrate synthase activity was 14.6% higher at highest versus lowest dissolved oxygen.