engleski

Influence of the Water Quality Parameters on the Condition Index of the European Flat Oyster Ostrea edulis

The condition index (CI) of oysters shows a seasonal variation which is mainly influenced by spawning season, as well as by relevant environmental factors. The temperature, inorganic nutrients and ammonia may affect oyster condition index, quantity and quality of the biofouling on the shell, as well as phytoplankton abundance. This paper describes the influence of different physical and chemical water quality parameters on the CI of cultivated European flat oyster Ostrea edulis in the Bistrina Cove, located in the Bay of Mali Ston, the location of the highest shellfish production area in Croatia. At the beginning of the experiment (January 2009) 1000 oysters of approximately the same size were selected and placed into plastic boxes. The boxes were deployed on the floating long-lines at the depth of 4 m. A sample of 30 specimens was taken for the CI calculation each second month during the one year period, together with water samples for the determination of the total ammonia nitrogen (TAN), phosphate, nitrate, nitrite, and sulphate concentration. Mean monthly value of the hydrographic parameters were calculated according to weekly measurements. The quantity of biofouling was measured after cleaning of sampled oysters shells. All measured parameters showed temporal variations during the year. Correlation coefficient between CI and nitrates was strongly positive (r=0.54). A strongly negative correlation was observed between CI and temperature (r=-0.68), and moderate with TAN (r=-0.488). CI showed low positive correlation with salinity (r=0.36) and sulphates (r=0.0397), and low negative with phosphates (r=-0.26). Relationship of CI were very low positive with nitrites (r=0.064), pH (r=0.01) and biofouling quantity (r=0.08), but very low negative with oxygen saturation (r=-0.18). These results indicate that among the measured water quality parameters, temperature, nitrates and TAN have the highest influence on the oyster condition index in the investigated area.

Ostrea edulis; condition index; water quality parameters

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