Stocking density estimations in sea bass fingerlings

Aquaflow Technical Leaflet 2003-142

European Network for the Dissemination of Aquaculture RTD Information (Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/

Acute changes in temperature and salinity occur in natural habitats, as well as in aquaculture facilities where environmental parameters cannot be entirely controlled. Metabolic costs in terms of oxygen consumption are affected by these environmental changes and also by the dissolved oxygen in the medium, which may become a limiting factor.

The oxygen consumption of fingerlings of the European sea bass, Dicentrarchus labrax, with a mean weight of 1.11g 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 Q₁₀ values (temperature quotient: influence of temperature changes of 10°C on the rate of reaction) ranging between 1.6 and 3.8. Salinity exposure was also applied stepwise (37-20-5-2-5-20-37ppt and 37-50ppt), 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 10h after the salinity change. After 48 hours of exposure no mortality was found in the salinity range of 3-30ppt, low mortality between 30 and 40ppt, and up to 100% mortality after hypersaline changes (40-60ppt).

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 0-50ppt, and for 1, 3, and 5g fingerling size classes. The aim of this model is to estimate the maximum stocking density on the basis of non-stressed conditions for the 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 this model. Increased oxygen demand due to temperature and salinity increases on one side and available dissolved oxygen concentrations on the other side are critical factors for aquaculture management procedures.

For more information:

Josef Dalla Via
Institut für Zoologie und Limnologie 
Universität Innsbruck
Technikerstrasse 25
6020 Innsbruck  - Austria

Fax: +43-(0)512-507-2930
E-mail: Josef.Dallavia@provinz.bz.it

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