Effects of hypoxia and hyperoxia on growth and food conversion efficiency in the spotted wolffish Anarhichas minor (Olafsen)

The effect of water oxygen content on growth and food conversion efficiency was evaluated for juvenile spotted wolffish, mean (+/- SD) initial weight 68.5 (+/- 17.5) g, reared at oxygen levels of 4.0, 6.0 (hypoxia), 9.6 (normoxia) and 14.5 (hyperoxia) mg L-1 for 11 weeks at 8 degreesC. Mean weights and total food consumption were significantly higher in the control and hyperoxic groups compared with the hypoxic groups at the end of the experiment. The 9.6 and 14.5 mg L-1 groups exhibited significantly higher overall specific growth rates (0.90 and 0.86% day(-1) respectively) compared with the groups on 4.0 and 6.0 mg L-1 (0.46 and 0.71% day(-1) respectively). In the hyperoxic group, growth was only limited in the first period and, in the hypoxic groups, growth rates increased throughout the experiment, with the 6.0 mg L-1 group performing equally well compared with the control in the last period. Overall, our findings suggest that the species will adapt to both high and low ambient water oxygen content given a period of adaptation. After the adaptation phase, growth and food conversion efficiency are comparable in the oxygen level range of 6.0-14.5 mg L-1 .