engleski

Mussel culture - influence of proximity to the fish farm

Simultaneous culture of several species in the same body water with the objective to optimize the use of different trophic levels is termed polyculture. Polyculture is traditionally applied in the fresh water pond aquaculture. In marine environments, polyculture of green mussel and salmon in same body water has been applied in New Zealand and Norway but is yet to be explored in the Mediterranean marine aquaculture. In fish cage culture in the Adriatic, mussel acts as an important filter feeder that removes excess of organic matter and is at the same time dominant fouling organism on farming facilities that needs to be removed. Environmental impact assessments and monitoring programs have demonstrated that influence of fish cages is localized. The question is, especially in oligotrophic environments, at which distance from fish cages culture of mussels culture needs to be. Experiment was set up in August 2005 on a seabass and seabream farm located on the south side of island of Pašman (middle Adriatic) to test hypothesis wheather fish farm proximity has influence on bivalve shell grow and condition index. Location one was immediately beside fish cages, location two 60 m away from fish cages and location three 700 m away from the cages. Lengths of 195 M. galloprovincialis were measured with vernier calipers to the nearest 0.1 mm and shells were individualy marked with mollusc tags (Hall print). Mean length of mussels used in growth experiment was 38.5± 1.75 mm. Marked shells were divided into three samples, placed in nylon net and suspended at pre-determined locations. After two months, mussels were removed from the water and their lengths were measured. For the analysis of condition index, unmarked mussels were kept in same type of net and at same locations. One and two months after start of the experiment 30 mussels were removed from each location and frozen for later analysis. Condition index was determined as ratio between cooked meat weight and sum of of cooked meat weight and shell weight. One-way analysis of variance was applied for data analyses. Prior to the analysis data were tested for homogeneity of variance. Turkey's test was applied for post hoc comparison. Results of the analysis showed that there was no statisticaly significant difference in shell growth between three locations (F=0.89, p=0.412). In two months, mussels grew on average 8.1± 2.69 mm. However, statisticaly significant differences were noted in condition index of mussels kept at different distances from the fish farm. In September, mussels from location 1 had significantly higher index than mussels kept at locations 2 and 3 (F=4.30, p=0.016, 1>2=3). In October, significant difference in condition index were observed between all three locations (F=30.09, p<0.001, 1>2>3). Due to a short duration of the study data presented must be considered preliminary. Future study should be conducted during the entire year.

aquaculture; bivalve; Mytilus galloprovincialis

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