engleski

Meat quality of European flat oyster Ostrea edulis in relation with variations of different environmental parametars in the bay of Mali ston

The quality of oyster meat shows a seasonal variation which is mainly influenced by spawning season, as well as by relevant environmental factors such as hidrographic parameters and the availability of food. It can also be affected by diseases and eventual water pollution (Ruiz et al., 1992 ; Austin et al, 1993 ; Gavrilović et al., 2008). One of the common methods for the evaluation of oyster quality is a determination of meat index (MI) according to Fleury et al. (2003). Following this method, in France which is the highest consumer of oysters in the world, this sea food product is classified into three categories: „spéciales“ (MI > 10, 5), „fines“ (MI 6, 5 – 10, 5) and „non – classées“ (MI < 6, 5). This paper describes the combined effects of different factors on the quality 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 level in Croatia. At the beginning of the experiment (January 2009) 1500 oysters of approximately the same size were selected and cemented on the nylon ropes (35 oysters per one rope) following local traditional farming techniques. Ropes were deployed on floating long-lines in the Bistina Cove in the Mali Ston Bay. Oysters were placed between one and four meters deep. A sample of 30 specimens was taken for the MI calculation each month during the one year period, together with water samples for the determination of the seston quantity parametars (total – TPM, inorganic – PIM and organic particulate metter POM). Mean monthly value of the hidrografic parametars were calculated according to a weekly measurement, where salinity and temperature were measured with a WTW Cond 315i/SET probe, pH with HANNA instrument HI 8424, and oxygen saturation with the OxyGuard Handy Polaris HO1P. For the quality of oyster meat, the MI was determined according to Fleury et al. (2003) with the formula: wet meat weight / total shellfish weight x 100. Seston quantity parameters (TPM, PIM, POM) were analyzed according to the method described by Peterson et al. (2003). According to the monthly values of the MI, oysters were classified following the categorization described by Fleury et al. (2003). Pearson correlation coefficients were calculated in order to determine the relationship between MI and each particular environmental parameter. The examination of the correlation between MI and all environmental parameters was calculated by multiple regression analysis (Zar, 1999). Results and discussion Figure 1. shows the monthly variations of MI. The highest value was recorded in April, followed by a decrease to the minimal recorded value in August. During the autumn months the value slightly increased until November. These variations coincided with the gonadal maturation seasons which occur two times per year in this aquatoria (Gavrilović et al., 2008). Fig. 1. Monthly variation of meat index of O. edulis in the Bistrina Cove A yearly average value of 12, 38 and the fact that oysters from this location belong in the category „spéciales“ for ten months in the year (only in August and September they were categorized as „fines“), leads to the conclusion that this location has favourable conditions for oyster cultivation. The French (IFREMER' s) method of monitoring (Fleury et al., 2003) at different locations resulted in MI values ranging from 6, 6 to 14, 6. Oysters at different farming location in Mali Ston Bay (Otok Života – Usko) were categorized as „spéciales“ for seven months in the year (Gavrilović et al., 2008). Correlation coefficients between MI and temperature showed a strong negative correlation (r=-0, 54). The relationship between MI and salinity (r=0, 32), TPM (r=0, 11) and POM (r=0, 14) were very low positive, while there was no correlation for POM (r=0, 01). MI and salinity had a very low positive correlation (r=0, 23), while there was a very low negative correlation between MI and oxygen saturation (-0, 11). According to the results of multiple regression analysis, the relationship between MI and all measured variables can be described by the following formulas: MI=-0.33*Month-0.15*T°C-0.02*Sal-0.07*O2+ 3.18*pH-93.65*TPM (r2=0, 99) MI=-0.447*Month-0.110*T°C+ 0.128*Sal-0.053*O2 + 2.414*pH+ 12.339*PIM-689.371*POM (r2=0, 99).

meat quality ; Ostrea edulis ; oyster ; environmental parametars

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