大口黑鲈对饲料中蛋氨酸需求量的评定

Assessment of dietary methionine requirement in largemouth bass,Micropterus salmoides

为了评定大口黑鲈对饲料中蛋氨酸的最适需求量,配制了蛋氨酸含量分别为0.61%,0.82%,0.98%,1.21%,1.42%和1.59%的6水平等氮等能饲料(44.39%粗蛋白质,0.30%胱氨酸,19.81kJ/g总能),以初始体重为(37.88±0.40)g的大口黑鲈为试验对象,进行了66d的饲养试验。饲养试验在室内循环水养殖系统中进行,每饲料处理设3个重复,每重复放养试验鱼25尾。饲养试验采取表观饱食投喂,每天投喂两次(8:30和15:30)。试验期间水温(27±1)℃,溶解氧6mg/L以上。结果表明,试验鱼的特定生长率、饲料效率、蛋白质效率、蛋白沉积率随着饲料中蛋氨酸水平从0.61%到1.21%的升高而显著提高(P<0.05),此后则呈降低的趋势。饲料中蛋氨酸水平对全鱼和肌肉中粗蛋白含量有显著影响(P<0.05);但各组间水分、粗脂肪和粗灰分含量差异不显著(P>0.05)。0.61%蛋氨酸的饲料组的肝体比和脏体比显著大于其他组(P<0.05),其他组间无显著差异(P>0.05)。饲料中蛋氨酸水平显著影响血清溶菌酶活力,头肾白细胞吞噬活性及其呼吸爆发活性(P<0.05)。以特定生长率为评价指标经二次回归分析得出,当饲料中的胱氨酸占饲料蛋白质的0.68%时,大口黑鲈对饲料中蛋氨酸的最适需求量为1.22%,占饲料蛋白质的2.75%。

A feeding trial was conducted to estimate the quantitative requirement of dietary methionine in largemouth bass[initial body weight （37.88±0.40） g].Six isonitrogenous and isoenergetic diets（ D1-D6） were formulated to contain 44.39% crude protein,0.30% cystine,19.81 kJ/g gross energy using plant protein and crystalline amino acids as the primary protein source to simulate the indispensable amino acid profile of largemouth bass muscle except for methionine under investigation.Six graded levels of methionine（ 0.61% ,0.83% ,0.98% ,1.21% ,1.42% ,and 1.59% ,respectively） at about 0.2% increment were achieved by adding zein-coated crystalline L-methionine at the expense of zein-coated crystalline glycine.Each diet was randomly assigned to triplicate tanks of 200-L capacity and 18 tanks were connected to a freshwater-flowing and air-aerated system in an aquiculture laboratory.In each tank,25 fish were fed by hand twice daily（ 8：30 and 15：30） to apparent satiation for 66 days.Water temperature was maintained at （ 27±1） ℃ and dissolved oxygen content kept about 6 mg/L.Light cycle was controlled under 12∶ 12 h.At the end of the trial,data analysis showed that specific growth rate（ SGR） ,feed efficiency rate（ FER） ,protein efficiency rate（ PER） ,protein deposition rate（ PDR） increased with increasing dietary methionine levels from 0.61% to 1.21% （ P0.05） and thereafter showed a declining tendency.The crude protein contents of whole body and muscle were significantly affected （ P0.05） by dietary methionine levels,while moisture,crude lipid and crude ash contents showed no significant differences（ P 0.05） .The hepatosomatic index and viscerosomatic index of fish fed D1 diet（ 0.61% methionine） were significantly higher than those of fish fed the other diets（ P0.05） .The serum lysozyme activity,phagocytosis activity and respiratory burst activity of head kidney leucocyte were significantly（ P0.05） affected by dietary methionine levels,which indicated dietary methionine level would also exert an effect on non-specific immunity in largemouth bass.A quadratic regression analysis about specific growth rate （ SGR） against dietary methinine level showed that the optimum dietary methinine requirement of largemouth bass was 1.22% of dry diet （ corresponding to 2.75% of dietary crude protein containing 0.68% cystine） .The present research may be helpful to formulating practical feed for largemouth bass.