Comparative study on the biochemical factors and antioxidant enzymes of rainbow trout eggs and larvae in a recirculating and flow-through system

Abstract

Recirculating aquaculture systems (RASs) may cause stressful conditions, by which the biochemical compositions and immune system of the fishes can be influenced. Thus, in this research, effects of water reusing on the biochemical compositions and antioxidant enzyme activities of rainbow trout (Oncorhynchus mykiss) eggs and yolk-sac larvae in an airlift-based recirculating system and a flow-through system were investigated. Eggs and larvae were sampled weekly at 1, 7, 14, 21, 28, 35, and 42 days after fertilization (DAF) in triplicate for analyses of both biochemical and antioxidant enzyme activities. The results indicated that there were no significant differences between the two systems in terms of the major biochemical composition of the eggs and larvae, except for the total lipid at 42 DAF, which was higher in the flow-through system. In both systems, the moisture values of samples increased progressively during the experimental period. The total lipid values in the embryonic stage (at 1, 7, 14, and 21 DAF) were statistically constant, whereas in the larval stage (at 28, 35, and 42 DAF), increased significantly in both systems. There were no significant differences between the systems and amongst the sampling times during the study period in terms of ∑SFA, ∑MUFA, and ∑PUFA. The values of TAC, SOD, CAT, and GPX in both systems were statistically constant during the embryonic stage, whereas there were significant differences between the embryonic and larval stages. In addition, the antioxidant enzyme activities revealed significant differences between the experimental systems, with an exception of the SOD activity, on which effects of treatment were not significant. In conclusion, there were no significant differences between the flow-through and airlift-based recirculating systems in terms of biochemical compositions, fatty acid profiles, and antioxidant enzyme activities during the embryonic stage. Thus, the designed recirculating system was practically efficient in this stage. While, the lipid content and antioxidant enzyme activities of the yolk-sac larvae reared under the recirculating system were respectively lower and higher than of the larvae reared under the flow-through system, which was more likely due to the accumulation of ammonia in the recirculating system.