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

Oxygen consumption of fingerlings of the European sea bass, Dicentrarchus l abrax, with a mean weight of 1.11 +/- 0.32 g, was measured in relation to a cute salinity and temperature changes. Stepwise acute temperature changes ( 25-20-15-10 degrees C and 25-30 degrees 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 p pt and 37-50 ppt), the metabolic rate overshooting by up to 80% of the rout ine level each time a salinity change occurred. The transient increase in m etabolic rate returned to pre-exposure levels within 3 to 10 h after the sa linity change. After 48 h of exposure no mortality was found in the salinit y range of 3-30 ppt, low mortality between 30 and 40 ppt, and up to 100% mo rtality after hypersaline changes (40-60 ppt). On the basis of the metaboli c data obtained, a model was constructed for maximum stocking density withi n the temperature range 10-30 degrees C, the salinity range 0-50 ppt, and f or 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 condi tions for fish. Fingerling activity, feeding, social interactions and handl ing stress induce higher metabolic rates in the fish and stocking densities have to be lowered. Thus, the optimum stocking density recommended under c ulture conditions is one-tenth of the calculated maximum stocking density b y our model. The implications of temperature dependent increases of oxygen demand and available disserved oxygen concentrations as critical factors fo r aquaculture management procedures are discussed in detail. (C) 1998 Elsev ier Science B.V. All rights reserved.