Larvae Growth and Biochemical Composition Change of the Pacific Oyster Crassostra gigas, Larvae during Artificial Seed Production

참굴 Crassostrea gigas 인공종묘생산 시 유생의 성장과 체성분 변화

A nutritional demand of oyster, Crassostrea gigas larva as part of research for improving of utilization of microalgae being used for the artificial oyster seed production. The change of body growth and biochemical compositions of larvae were investigated during larvae rearing in hatchery. The larvae were cultured in 60 M/T tank and fed mixture 6 different phytoplankton species, Isochrysis galbana (30%), Cheatoceros gracilis (20%), Pavlova lutheri (20%), Phaeodactylum triconutum (10%), Nannochryis oculata (10%) and Tetraselmis tetrathele (10%). The initial feeding amount was $0.3{\times}10^4cells/mL$ at three times a day to D-shaped larva and the feeding amount had been increased 30% gradually every two day since the larvae were raising. The larvae were developed from D shape to pediveliger stage for 12 days. The daily growth of shell length and hight were $5.8{\sim}30.8\;{\mu}m$ and $8.7{\sim}31.4\;{\mu}m$, respectively and weight gains were changed from D shape to pediveliger as follow: wet weight was $0.52{\sim}15.0\;{\mu}g/larva$, dry weight was $0.2{\sim}6.5\;{\mu}g/larva$, and ash free dry weight was $0.1{\sim}8.5\;{\mu}g/larva$. The larvae growth pattern shown a logarithmic phase from D shape to umbone stage but after that stage shown a exponential growth aspect. The crude protein, crude lipid and nitrogen free extract (NFE) of larvae during rearing periods were analyzed as $6.1{\sim}10.6%$, $0.6{\sim}1.1%$ and 1.0-2.7%, respectively. And the total amino acid contents of the larvae during rearing periods were in order as glutamic acid $1.26{\sim}2.24%$, aspartic acid $0.97{\sim}1.70%$, and methionine $0.12{\sim}0.33%$. Of the total fatty acid in the analyzed larvae, the saturated fatty acid (SSAFA) was decreased from 54.3% (D shaped larvae) to 17.1 % (pediveliger) as larvae development but the total mono-unsaturated fatty acid (${\Sigma}MOFA$) and Poly-unsaturated fatty acid (${\Sigma}PUFA$) were increased from 29.9% and 7.8% to 40.6% and 45.6%, respectively. By the way the each fatty acid of the larvae were composed of palmitic acid $9.89{\sim}36.95%$, oleic acid $12.17{\sim}32.29%$, linoleic acid $1.96{\sim}33.55%$, EPA $2.17{\sim}11.58%$ and DHA $1.95{\sim}4.51%$. As a result of this study, the larvae of oyster were demanded a various nutrients for healthy growth and the feeding control, expecially after umbone stage larvae are a rapidly growing time, is very important for success of artificial seed production.

참굴 유생의 최적 성장과 먹이생물의 이용성을 높이기 위해 현재 인공종묘생산에서 많이 이용되고 대량배양이 용이한 미세조류를 대상으로 그 요구조건을 구명하고, 나아가 인공배합사료개발에 요구되는 기초적인 사료 설계 자료를 얻기 위하여 대량 인공종묘생산 시 유생에 축적되는 영양소의 변화를 유생의 발달 단계에 따라 조사하였다. 유생의 일간 각장 성장은 $5.8{\sim}30.8\;{\mu}m$로 중형각정기 유생 이후 최대 성장률을 보였고, 사육 12일째 각장 $311.0\;{\mu}m$의 부착기 유생으로 성장하였다. 습중량, 건중량 및 AFDW는 각각 $0.5{\sim}15.0\;{\mu}g/larva$, $0.2{\sim}6.5\;{\mu}g/larva$ 및 $0.1{\sim}2.3{\mu}g/larva$이었다. 각각의 증중량은 D형 유생에서 각장 $100\;{\mu}m$까지는 감소하였고, 사육 8일째까지는 급격한 증가를 보였지만, 부착기 유생으로 발달하면서 감소하였다. 알의 일반성분 조성 중 회분은 7.7%로 전체 유생단계의 $30.3{\sim}39.6%$에 비해 매우 낮은 함량을 보였지만, 조단백질, 조지질 및 탄수화물의 함량은 전 유생단계에 비해 높았다. 유생의 조지질($0.6{\sim}1.1%$), 조단백($6.1{\sim}10.6%$), 탄수화물($1.0{\sim}2.7%$), 아미노산 및 지방산 함량은 포기각정기 유생까지는 감소하였고, 이후 어느 정도 축적되는 경향을 보였다. 알과 유생의 아미노산 조성 비율은 유생의 발달단계와 상관없이 비슷한 조성비로 glutamic acid (5.85%, $1.26{\sim}2.24%$)과 aspartic acid (4.67%, $0.97{\sim}1.70%$)가 가장 놀은 조성을 보였다. 전체 유생기 동안 필수아미노산으로서 leucine ($0.83{\sim}1.26%$), lysine ($0.90{\sim}1.35%$) 및 arginine ($0.92{\sim}1.25%$)이 성장함에 따라 비교적 높게 축적되었다. D형 유생에서 부착기 유생으로 발달하는 과정에서 조화지방산은 65.5% ($54.3{\rightarrow}17.1%$)로 줄어들었고, 단일불포화지방산과 고도불포화지방산은 각각 35.8% ($29.9{\rightarrow}40.6%$)와 484.6% ($7.8{\rightarrow}45.6%$)로 축적되었다. 이 중 palmitic acid ($9.9{\sim}37.0%$), oleic acid ($12.2{\sim}32.3%$) 및 linoleic acid ($2.0{\sim}33.6%$)가 비교적 높은 조성을 보였고, EPA와 DHA은 각각 $2.2{\sim}11.6%$, $2.0{\sim}4.5%$로 나타나, 전체 유생단계에서 EPA가 DHA에 비해 높은 조성비($1.1{\sim}3.5$, EPA/DHA)을 보였다.