The effect of CO2, total ammonia nitrogen and pH on growth of juvenile lumpfish (Cyclopterus lumpus)

The objective of this study was to examine the effects of CO2, total ammonia nitrogen (TAN: nitrogen bound as either NH3 or NH4+) and pH on the growth and survival of juvenile lumpfish in a two-month growth study. The results demonstrate the complex interactions of these water quality variables. The specific growth rate (SGR) of the lumpfish was progressively reduced with increasing [CO2] concentration above 5–10 mg·L−1. However, growth may be reduced at even lower [CO2] and the results provide no clear safe limits under which the growth of lumpfish is unaffected by CO2 concentration. At the lowest [CO2] tested (8 mg·L−1) the SGR was reduced compared with controls. Moreover, in treatments where the [CO2] concentration increased to 8 mg·L−1 as pH was artificially reduced, the SGR was similarly reduced. These results indicate that lumpfish juveniles are very sensitive to increased [CO2] concentration in water. The SGR of the lumpfish was progressively reduced as the NH4+ concentration increased while maintaining the [NH3] constant (70–80 μg·l−1). However, in these treatments the [CO2] also increased to 8–10 mg·L−1 due to changes in pH and this likely contributed to reduced growth. Moreover, due to nitrification in the rearing systems, the nitrite concentration also increased to critical levels (1.5–4.2 mg·L−1) that could affect growth. Therefore, the results do not provide clear evidence for effects of increased NH4+ on the growth of lumpfish. Taken together, the results of the experiments show that lumpfish are sensitive to perturbations in water quality and provide a benchmark for operational welfare indicators in lumpfish aquaculture.