Abstract
Feeding trials were conducted to determine the essentiality of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and to compare the efficiency between EPA and DHA for juvenile Korean rockfish. Fish averaging 2.1 g were fed experimental diets containing different levels of EPA or DHA, and different combinations of EPA and DHA in two separate experiments. Graded levels ($0.0{\sim}l.75\%$) of dietary EPA or DHA as ethyl esters were substituted for a part of the $8\%$ beef tallow in the basal diet. After 5 weeks of the experimental period, weight gain, chemical composition of whole body, protein and lipid retention efficiency, hepatosomatic index, and fatty acid composition of liver were measured. Daily growth rate and feed efficiency were the lowest in fish fed the diets without EPA arid DHA. These responses were effectively improved by increasing EPA or DHA in the diets up to $1.0\%$ levels, and then reached a plateau between 1.0 and $1.75\%$ levels of either EPA or DHA. Protein and lipid retention efficiency were also improved with the high levels of dietary EPA or DHA. DHA was superior to EPA at the same level of each in weight gain, feed efficiency, and protein and lipid retention efficiency. Hepatosomatic index tended to decrease with increase of the dietary EPA or DHA levels. Lipid contents of whole body were increased with levels of EPA or DHA in the diets. Dietary EPA and/or DHA levels affected directly the fatty acid composition of liver polar lipid. EPA or DHA in the liver polar lipid were increased with levels of dietary EPA or DHA, respectively, whereas those in nonpolar lipid were not affected by the dietary levels of EPA and/or DHA. These finding indicate that either of the EPA or DHA is essential for normal growth of Korean rockfish, and the essential fatty acid requirement is $1.0\%$ of EPA and/or DHA in the diet. DHA is superior to EPA as essential fatty acid, and the dietary EPA/DHA ratio of less than 1.0 may be adequate for normal growth of Korean rockfish fed a diet enough n-3HUFA (EPA and DHA).
조피볼락 사료의 EPA 및 DHA 필수성과 적정 EPA/DHA 비를 구명하기 위해, 기본 지질을 우지로 하여 EPA와 DHA를 각각 $0{\sim}1.75\%$ 첨가한 사료와 EPA/DHA 비를 다르게 첨가한 사료 18종을 제조하여 조피볼락 치어(평균 체중 2.1 g)를 대상으로 5주간 사육 실험한 결과는 다음과 같다. 일간증중율(EPA 사료: $2.39{\sim}3.66\%$, DHA 사료: $2.39{\sim}3.72\%$)과 사료효율(EPA 사료: $73{\sim}97\%$, DHA 사료: $73{\sim}100\%$)은 EPA 및 DHA 사료 모두 사회중의 함량 $1.0\%$까지만 증가하고 그 후에는 일정한 값을 나타내어, EPA 및 DHA 요구량이 모두 $1.0\%$로 추정되었다. 단백질축적효율(EPA 사료: $23.3{\sim}32.6\%$, DHA 사료: $23.3{\sim}35.9\%$)과 지질축적효율(EPA 사료: $82.2{\sim}109.5\%$, DHA 사료: $82.2{\sim}112.1\%$)도 사료의 EPA 또는 DHA가 증가할수록 증가하였다. 이러한 결과들은 EPA 사료에서보다 DHA 사료에서 전반적으로 좋은 반응을 보였으며, EPA/DHA 사료에서도 EPA에 대한 DHA 비가 1.0 이상인 사료에서 양호한 결과를 보였다. 전어체의 단백질 함량은 큰 변화가 없었지만 지질 함량은 사료의 EPA 및 DHA가 증가할수록 약간씩 증가하는 경향을 나타내었다. 간중량비는 사료의 EPA 및 DHA 함량이 증가함에 따라 감소하였으며, DHA 사료가 EPA 사료보다 대체로 낮은 값을 보였다. 사료의 EPA가 증가함에 따라 간 극성지질의 EPA ($0.4{\sim}4.3\%$) 함량은 증가하였으나DHA ($0.2{\sim}l.0\%$) 함량은 거의 증가하지 않았고, 사료의 DHA 증가와 더불어 간 극성지질의 DHA ($1.0{\sim}6.4\%$) 함량은 증가하였으나 EPA ($0.2{\sim}0.5\%$) 함량은 증가하지 않았다. 반면, 간 비극성지질의 지방산조성은 사료 지방산조성에 영향을 거의 받지 않아 변화 폭이 적었다.
(Fish Culture Division, National Fisheries Research and Development Agency)
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