Effect of seawater pH on selected blood biochemical parameters of juvenile turbot Scophthalmus maximus (Linnaeus, 1758)

Abstract

The effect of seawater pH on blood physiology in juvenile turbot Scophthalmus maximus (Linnaeus, 1758) reared in recirculating aquaculture systems (RAS) was examined. S. maximus (19.89±0.25 g) were exposed to six pH levels at 6.3±0.2, 6.8±0.2, 7.3±0.2, 7.8±0.2, 8.3±0.2 and 8.8±0.2. Haemoglobin content (HBC) at acidic conditions was higher compared to that under alkaline conditions. The frequency of total nuclear anomalies (FTNA) was high at pH levels below 7.3 or above 8.3. The relationship between FTNA and pH was well described using a quadratic equation. Alkaline phosphatase activity was significantly declined at pH above 8.3, while total superoxide dismutase activity (T-SOD) remained virtually unchanged among all treatments. This study demonstrated that HBC and FTNA can be used as reliable biomarkers to evaluate the effect of pH in aquatic ectotherms from physiological standpoints. Our findings suggest that environmental pH in RAS ranging from 6.8 to 7.8 is appropriate for juvenile turbot aquaculture.