Effects of Dissolved Carbon Dioxide on Cataract Formation and Progression in Juvenile Atlantic Cod, Gadus morhua L.
This study was partly funded through an NOAA National Marine Aquaculture Initiative Grant (Award #: NA08OAR4170829 to Great Bay Aquaculture).
In this study, the effects of elevated levels of dissolved carbon dioxide were investigated in a marine recirculation system on the development of cataracts in juvenile Atlantic cod, Gadus morhua. Replicate groups (n = 9), at an initial average weight of 23.5±0.8 g, were exposed to one of the three levels of dissolved CO2: low (6.99±0.021 mg/L), mid (12.23±0.013 mg/L), or high (19.77±0.029 mg/L) for 5 mo. Fish were sampled every 30 d to measure growth and assess cataract status. Fish in all CO2 treatments developed cataracts, but cataract prevalence (%) was significantly higher after 5 mo in fish from the high CO2 (97.8±2.4%) than mid (60.7±9.1%) or low CO2 (29.6±8.1%) treatments.
Cataract severity, graded on a scale of 0–8, showed a similar pattern with average cataract scores of 6.0±0.3, 3.0±0.5, and 1.2±0.3 for fish in high, mid, and low CO2 treatments, respectively. Survival was reduced in the high CO2 treatments (94.5%) compared to the low CO2 treatments (97.6%). Lengths were significantly smaller in the high CO2 treatment fish after 5 mo (217.9±5.2 mm) than either mid (231.1±3.1mm) or low CO2 (236.0±4.5mm) treatments.Weights of the fish followed a similar pattern with the fish in the high CO2 treatments weighing significantly less after 5 mo (91.6±7.8 g) than fish in the low CO2 treatment (126.7±8.8 g). Condition factor, specific growth rate, and feed conversion ratio were also negatively affected by increasing levels of CO2 but by the end of the trial, these values were comparable to those of the low and mid CO2 treatments. These results demonstrate that elevated levels of dissolved CO2 significantly affect the performance of Atlantic cod in a production setting and leads to the development of cataracts. Although the physiological mechanism of CO2-induced cataract formation remains unknown, the results from this study suggest that levels of dissolved CO2 must be given more attention in order to avoid potentially negative consequences on the growth, eye health, and survival of juvenile Atlantic cod.