Oxygen consumption in sea bass fingerling Dicentrarchus labrax exposed to acute salinity and temperature changes: metabolic basis for maximum stocking density estimations

Abstract

Oxygen consumption of fingerlings of the European sea bass, Dicentrarchus labrax, with a mean weight of 1.11±0.32 g, was measured in relation to acute salinity and temperature changes. Stepwise acute temperature changes (25–20–15–10°C and 25–30°C) induced a strong increase of the temperature dependent metabolic rate, with Q 10 values ranging between 1.6 and 3.8. Salinity exposure was also applied stepwise (37–20–5–2–5–20–37 ppt and 37–50 ppt), the metabolic rate overshooting by up to 80% of the routine level each time a salinity change occurred. The transient increase in metabolic rate returned to pre-exposure levels within 3 to 10 h after the salinity change. After 48 h of exposure no mortality was found in the salinity range of 3–30 ppt, low mortality between 30 and 40 ppt, and up to 100% mortality after hypersaline changes (40–60 ppt). On the basis of the metabolic data obtained, a model was constructed for maximum stocking density within the temperature range 10–30°C, the salinity range 0–50 ppt, and for 1, 3, and 5 g fingerling size classes. The present aim of this model is to estimate the maximum stocking density on the basis of non-stressed conditions for fish. Fingerling activity, feeding, social interactions and handling stress induce higher metabolic rates in the fish and stocking densities have to be lowered. Thus, the optimum stocking density recommended under culture conditions is one-tenth of the calculated maximum stocking density by our model. The implications of temperature dependent increases of oxygen demand and available dissolved oxygen concentrations as critical factors for aquaculture management procedures are discussed in detail.