Effects of Dissolved Carbon Dioxide on Cataract Formation and Progression in Juvenile Atlantic Cod, Gadus morhua L

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 CO₂treatments 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 CO₂treatments, respectively. Survival was reduced in the high CO₂treatments (94.5%) compared to the low CO₂treatments (97.6%). Lengths were significantly smaller in the high CO₂treatment fish after 5 mo (217.9 ± 5.2 mm) than either mid (231.1 ± 3.1 mm) or low CO₂(236.0 ± 4.5 mm) treatments. Weights of the fish followed a similar pattern with the fish in the high CO₂treatments weighing significantly less after 5 mo (91.6 ± 7.8 g) than fish in the low CO₂treatment (126.7 ± 8.8 g). Condition factor, specific growth rate, and feed conversion ratio were also negatively affected by increasing levels of CO₂but by the end of the trial, these values were comparable to those of the low and mid CO₂treatments. These results demonstrate that elevated levels of dissolved CO₂significantly 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 CO₂must be given more attention in order to avoid potentially negative consequences on the growth, eye health, and survival of juvenile Atlantic cod.