实验微粒饲料中花生四烯酸含量对牙鲆(Paralichthys olivaceus)仔稚鱼生长、存活的影响

EFFECTS OF DIFFERENT CONTENTS OF ARACHIDONIC ACID IN EXPERIMENTAL MICRODIETS ON GROWTH AND SURVIVAL OF LARVAL JAPANESE FLOUNDER PARALICHTHYS OLIVACEUS

采用花生四烯酸即廿碳四烯酸(AA,20∶4n-6)含量梯度法,制备了四种n-3HUFA含量相等、DHA/EPA比例相同、AA含量分别为0.06%、1.00%、1.5%、2.0%的实验微粒饲料,进行了AA的不同含量对牙鲆仔稚鱼生长、存活、体内相关成分以及对外部压力耐受性的影响研究。26天的养殖试验结果表明,当牙鲆仔稚鱼实验微粒饲料中AA的含量为1.5%时,牙鲆仔稚鱼的生长、存活以及对不同压力的耐受性都达到最佳。养殖试验结束后,对稚鱼体内相关成分的分析结果表明,稚鱼体内AA的含量随着实验微粒饲料中AA含量的增加而增加。

The n-6 highly unsaturated fatty acids （n-6HUFAs）, just like n-3 ones （n-3HUFAs）, are essential to marine larval fish for their growth and survival. However, at present, its importance has not yet been fully emphasized in the study on the nutrition of marine larval fish. Arachidonic acid （AA）, a type of n-6HUFAs, was studied based on few available reports to reveal the effects of AA on the growth and survival of larval Japanese flounder Paralichthys olivaceus fed with microdiet. The feeding experiment was designed in different contents of AA in experimental microdiets and to find out the relation between the content and the growth and survival of the flounder, and their tissue compositions and tolerance against different ambient stresses. Four formulated experimental microdiets were made containing at AA dietary contents of 0.06%, 1.00%, 1.50% or 2.00%, respectively, with same proportions of n-3HUFA and DHA/EPA. Major base of the formula for the four microdiets consisted of special fish meal 74% （dry weight）, mixed oils 10%, mixed vitamins 5.4 %, mixed minerals 4.5 %, phagostimulant 3.0 %, and binders 3.1%. Larval fish were divided into four groups. And each group was subdivided in two containers at 200 each. Before experiment start, 40 were randomly picked for measuring the length, yielding mean total length of 4--5mm. The experiment began on May 24th, 2004, and ended on June 18th, 2004, lasted 26 days. The temperature of seawater was 17.5-21.5℃, pH 8.2-8.3, salinity 33, with continuous aeration. Water in the containers were changed by 1/2-4/5 daily. After the experiment, tests on low oxygen and high salinity were carried out to check the tolerance of larval fish to different stresses. The total length of every fish was measured by hand, and the survival rate of larval fish in every container was counted. Meanwhile, the contents of fatty acids in the fish bodies were measured by gas chromatography. All the data were analyzed statistically. The results showed that, when AA increasing from 0.06 % to 1.5 % in the microdiets, the mean total length of the fish increased from （11.83 ± 1.04）mm to （13.58 ± 1.08）mm, and the survival percentages of them were from （35.75 ± 2.40）% to （44.75 ± 2.49）%. However, when AA content increased from 1.5% to 2.0%, the mean total length reduced to （12.50±0.79） ram, and the survival rate to （32.00 ±2.33）%. The low-oxygen test and high-salinity test showed that, at 1.5% of AA content in experimental microdiet, the survival rate was the highest （100% and 95%, respectively）. The AA contents in the fish bodies increased synchronically with those in the experimental microdiets, shown in our measurement. Therefore, under the experimental conditions, the optimal content of AA in microdiet for larval Japanese flounder was about 1.5 %.