Potential interactive effects of ammonia and CO2 on growth performance and feed utilization in juvenile Atlantic cod (Gadus morhua L.)

To study the isolated and combined effects of unionised ammonia (UIA-N) and CO2 in water on juvenile Atlantic cod, fish were exposed to four different treatments: moderate levels of CO2 (10 mg L− 1); moderate levels of NH3 (0.06 mg L− 1 UIA-N); a combination of CO2 (10 mg L− 1) and NH3 (0.06 mg L− 1 UIAN) and a control treatment without added CO2 or NH3, for 41 days. The final weight of the groups exposed to either CO2 or NH3 were not significantly different from the control group, where 22% weight gain was observed during the course of the 41-day exposure time. Minor differences in SGR were observed during the first growth period, but not later, between the control and the CO2 and NH3 groups, suggest that the fish were able to adapt to the conditions over time. However, no weight gain and lower feed intake was observed in the group exposed to both CO2 and NH3. To create identical [UIA-N] for the NH3 and CO2 + NH3 groups it was necessary to double the [TAN] for the latter group due to lower pH resulting in doubling of [NH4+]. It is suggested, that the high [NH4+] to which the CO2 + NH3 group was exposed may have caused the reduced growth.