engleski

Variation of non-specific esterase activity in the digestive system of European flat oyster Ostrea edulis in relation to food availibility and codition index

A more thorough knowledge of the variations of digestive enzyme activities is essential for understanding shellfish physiology and its interaction with environmental conditions. The quality of oysters, usually measured by a condition index (CI), shows a seasonal variation which is mainly influenced by, in addition to spawning season, relevant environmental factors such as food availibility and water quality. This paper describes monthly variations of non-specific esterase activity (EA) in the digestive system of the european flat oyster Ostrea edulis, a species of high market value, in relation to food availibility and product quality under natural growth conditions. At the beginning of the experiment 2000 oysters of approximately the same size were selected and cemented on nylon ropes following local traditional farming techniques. Ropes were deployed on floating long-lines in the Mali Ston Bay. A sample of 60 specimens was taken for the histochemical detection of EA, as well as CI calculation for each month during the one year period. Water samples were collected for the determination of seston quantity parameters (total – TPM, inorganic – PIM and organic particulate matter - POM) according to Peterson et al. (2003). Samples for histochemical detection of EA (E.C.3.1.1.) were immediately fixed in cold formol–calcium for 24 h and then transferred to a ice-cold sucrose solution. The tissues were sectioned in a cryostat into10 µm thickness and were processed for histochemical detection of EA according to Loyda et al. (1979), where 1-naphtyl-acetate (pH 6, 5) was used as substrate. Enzymatic activity was visually analysed for each part of the digestive system (stomach, digestive ducts, digestive tubules, mid-gut) and further described according to the observed intensity of colour reaction by numbers from 0 to 4. The CI was determined according to the formula: dry meat weight / dry shell weight x 1000. The examination of the correlation between non-specific esterase activity and measured parameters was determined by multiple regression analysis (MRA). The EA shows different intensity in different parts of the digestive system. The highest activity during the entire year was recorded in the digestive tubules and mid-gut, whilst the lower activity was detected in the stomach and digestive ducts. In addition, the highest activity in all parts was recorded in June, September and October, and the lowest from January to April and at the end of the year. According to the results of MRA, the relationship between EA in each part of the digestive system and food availibility, as well as CI, can be described by the following formulas: EAStomach = 2750.75*PIM - 1042.43*POM, r2=90.38 EATubules = 3703.54*PIM - 1438.49*POM, r2= 91.47 EADucts = 2998.48*PIM - 1198.94*POM, r2= 92.96 EAMid-gut = 2887.15* PIM - 899.613 *POM, r2= 91.24 EAStomach = 0.0593467*CI, r2= 85.74 E Tubules = 0.0754942*CI, r2= 80.98 E Ducts = 0.0598162*CI, r2= 83.22 EMid-gut = 0.0744833*CI, r2=91.45

non-specific esterase; oyster; O. edulis

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