Comparison of stress markers of rainbow trout (Oncorhynchus mykiss) reared in earthen saltwater pond and fiberglass freshwater tanks

The aim of this study was to compare stress responses of rainbow trout reared in saltwater earthen ponds and freshwater fiberglass tanks. To this, 10000 fish were distributed in a three-ha earthen pond and 150 fish in three fiberglass tanks (2000L). Blood samples were taken after 3 months rearing. The source of fish and feed was similar between the saltwater pond and fiberglass tanks. In the blood samples, concentrations of cortisol, glucose, lactate, lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) were determined. There was no significant difference in water temperature, dissolved oxygen and pH between the pond and tanks; however, water salinity and ammonia was higher in the pond compared to the tanks. Serum cortisol, glucose, lactate, LDH and AST of the fish in earthen ponds were significantly higher than those of the fish reared in fiberglass tanks. The results suggest that the fish in the earthen pond experienced higher stress, which could be due to water salinity and ammonia. As a result, it suggested that hygienic and managerial approaches are particularly followed when trout are reared in earthen saltwater ponds to prevent disease outbreak.