engleski

IMPACT OF TUNA FISH FARM IN THE ADRIATIC SEA (CROATIA) ON THE WATER QUALITY

The potential impacts of aquaculture are wide, ranging from aesthetic aspects to direct pollution. The degree of impact of the wastes from the cage aquaculture is dependent on the species, culture method and feeding techniques. Despite the large number of studies about aquaculture impacts on water quality, very little information is available for an environmental impact assessment and environmental monitoring of tuna fattening. The key environmental impacts of tuna fattening are related to feeding and excretion, which is high due to the use of fresh and defrosted fish. The fact that Croatia is one of the main capture-based tuna aquaculture producers in Mediterranean initiated the present study. The general aim of the study was to assess the impacts of tuna fattening in the Adriatic Sea based on the microbial analysis. The specific objective was to identify the indicator bacteria as suitable indicators for tuna farming impacts. To achieve these goals, we have conducted the study at two sampling sites, tuna fish farm in the East Adriatic Sea and approximately 500 m distant control site, both in the time of normal and reduced feeding regime. The distribution of microbial indicators (heterotrophic bacteria, total coliforms, faecal coliforms, E. coli, enterococci and Vibrio) in the water was determined at different depths (surface, 3 m and bottom) and seasons (spring and autumn). In our study both faecal coliforms and enterococci showed values higher than those previously reported. Determined faecal coliforms/enterococci ratio indicates animal origin of faecal indicators, probably seagulls. During reduced feeding regime ratio has changed due to decreased number of seagulls what confirmed our presumption. Bacterial contamination with seagull’s faeces is an important feature. The results indicate that concentrations of microbial indicators represent a quite sensitive descriptor of the initial impact of tuna farm on the environment. The findings of our study, with combination of previously existing knowledge, should be the basis for monitoring of tuna farm impacts in general.

Tuna fish farm; water quality; Croatia

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