탄소 및 질소 안정동위원소비와 지방산 생체지표를 이용한 바지락의 크기별 및 계절별 먹이원 연구

Abstract

Manila clams sampled in Seonjae Island, Korea with shell lengths (SL) below 19.76mm in average showed a significantly depleted carbon and nitrogen isotope values (P<0.05) by 0.80~1.41‰. This size related variation can be caused by either altered carbon and nutrient source or by affected isotopic incorporation rates and discrimination factors as illustrated by Martinez del Rio et al. (2009). In order to examine size-related diet shift in manila clams, R. philippinarum with different sizes that were constantly fed on known mixed microalgae for several months were sampled from Incheon Fisheries Hacheries Research Institute (IFHRI). These manila clams have shown a high intra-species variation in growth rate with a maximum difference of more or less 2.30cm. The smallest size groups (3.68±0.17 mm and 6.88±0.21 mm) obtained their nutrition from both P. tricornutum and aggregated organic matter that consists of dead or decomposed microalgae or other detritus. Bigger size groups (10.92±0.34 mm and 14.81±0.25 mm) obtained most of their energy from P.tricorutum and also from other phytoplankton unlike the biggest size group (21.15±1.02 mm) that feeds mainly on fresh microalgae of all diets fed. This variation in diet reveals that smaller clams mostly inhale dead or decomposed microalgae that sinks on the bottom while the bigger clams uptake more fresh ones that are still alive. This variation in feeding behavior could have been caused by morphological constraints such as limited siphon length.To compare fatty acid composition of manila clams with different sizes, a more significant contribution of flagellates and ciliates was revealed in bigger size and diatom in smaller size clams. The results suggest that manila clams greater than and below 19.76mm in average have different feeding behavior and P. tricornutumand I. galbanawere the two most preferred diets for manila clams cultured in IFHI. Fast-growing manila clams have lower concentration of fatty acids because they would use up their energy in a greater amount to meet higher scope for growth.