Escapes of fish from sea cage installations raise a...

European sea bass (Dicentrarchus labrax), an important species for the Mediterranean aquaculture industry, has been reported to escape from sea cage installations. Fish escapes are caused mainly by operational and technical failures that eventually create tears. Escapees may interact with wild stocks through interbreeding, transfer of pathogens and competition for food. The aim of this study was to examine to what extent the presence of a visible obstacle close to a tear in the net influences sea bass propen-sity to escape. Fish were initially confined into small sea cages, with a tear on one side. The escape behaviour was tested under experimental conditions. It is clearly demonstrated that sea bass were able to locate a tear in the net pen, immediately after its appearance. Crossings occurred in all cages, in singles or in a series of up to seven individuals. The presence of an obstacle close to the net tear altered the escape behaviour of D. labrax, resulting in a delay that eventually reduced the escape rate. To conclude, it is highly recommended that sea bass cages should be kept internally the culture array. Furthermore, the placement of artificia