Physiological stress responses of sea bass (Dicentrarchus labrax) to hydrogen peroxide (H2O2) exposure

Hydrogen peroxide (H2O2) is currently being considered as a potential disinfectant in aquaculture. Stress impact of H2O2 exposure in sea bass, Dicentrarchus labrax was evaluated by measuring stress indicators; plasma cortisol, lactate, glucose, plasma calcium (Ca), phosphorus (P), sodium (Na), potassium (K), chloride (Cl), magnesium (Mg), hematocrit, hemoglobin, total protein and albumin. The stress indicators were analysed for 30 fish from each of three experimental groups: (i) exposure group: fish that were sampled immediately after a 1 h 50 ppm H2O2 bath, (ii) recovery group: fish treated as in (i) and sampled after a 24 h recovery period without H2O2, and (iii) control group: fish that were sampled at the same time as exposure group fish, but that were not exposed to H2O2. The stress indicators measured were compared against the control. Plasma cortisol and hemoglobin levels were significantly higher than control, after H2O2 exposure and after the 24 h recovery. Plasma lactate level was significantly higher after H2O2 exposure, but similar to control levels after the 24 h recovery. Plasma glucose level was significantly higher after H2O2 exposure and significantly lower than the control at 24 h. Plasma electrolytes showed different responses to H2O2 exposure. Plasma Ca, Na and Mg were significantly higher in the exposure group compared to the control and at 24 h, plasma Ca and Mg were similar to the control while plasma Na was significantly lower than control. There were no changes in plasma P, K and Cl as a consequence of H2O2 exposure, but plasma K and Cl were significantly increased at 24 h. Hematocrit and albumin were significantly increased after H2O2 exposure and similar to the control at 24 h. The results indicate a quick physiological stress response and sensitivity of sea bass to H2O2 exposure, which appears to require more than 24 h period for full recovery.