Welfare status of cage farmed European sea bass Dicentrarchus labrax: a comparison between submerged and surface cages

As alternative farming methods, we investigate growth, haematological, biochemical and immunological parameters of European sea bass (Dicentrarchus labrax) farmed in submersible cages in order to compare physiological status under different rearing conditions and to validate the efficacy of submersible technology in solving several of the substantial problems that exist in surface-based fish farming as heavy storms, algal and jellyfish blooms and attacks by predators. The study was conducted in 2008 in the Gulf of Castellammare (NW Sicily, Mediterranean Sea) in two submerged and two surface cages filled with 75.000 D. labrax (initial weight: 28.2 4.3 gr), for each cage. No significant differences were shown in specific growth rate between the two groups, even if, fish cultured in submerged cage reached the largest size. Results from biochemical and haematological parameters examined indicated higher welfare state in fish cultured in submerged cages. Fish reared in surface cages showed a significantly higher blood cortisol and glucose levels and haematocrit value than those of submerged cages. Also lysozme and haemolytic activity, used as indicators of immunocompetence in fish exposed to stress, lead us to suppose that submergence could have a positive effect on some components of innate immune system of cultured fish. Results of this study suggest mariculture in submerged net cages a promising system that allows to minimize stress and therefore that favours animal welfare.