黑鲷幼鱼赖氨酸需求量的研究

选用初体重(9.13±0.09)g的黑鲷(Sparus macrocephalus)幼鱼360尾随机分为6组,每组3个重复,每个重复20尾,分别投饲赖氨酸水平实测值为2.08%、2.52%、2.88%、3.25%、3.68%和4.05%的等氮等能日粮.试验期为8周,观察日粮赖氨酸对黑鲷生长性能,体组成以及消化能力的影响,并确定其适宜的赖氨酸需求量.结果表明,当饲料中的赖氨酸水平从2.08%上升到3.25%,黑鲷的增重率和特定生长率随着饲料赖氨酸水平升高而升高(P<0.05),此后则出现降低的趋势.赖氨酸低水平组(2.08%和2.52%)饲料效率较其他组低(P<0.05),其余各组之间没有显著性差异(P>0.05).饲料赖氨酸水平从2.08%上升到3.25%,蛋白质沉积率有显著提高(P<0.05),此后趋于稳定.存活率与肝体比与赖氨酸水平无关.全鱼蛋白质含量随饲料赖氨酸水平增加而增加,脂肪含量则呈现下降趋势;各组间的灰分和水分含量没有显著性差异(P>0.05).肝脏总必需氨基酸和赖氨酸含量随着饲料赖氨酸水平升高而增加,但是在赖氨酸添加水平最高组这两个指标均有所降低(P<0.05).随着饲料赖氨酸含量增加,血清胆固醇含量、谷丙转氨酶(ALT)和谷草转氨酶(AST)活性呈下降趋势,赖氨酸含量为3.68%时均达最低值,而对血清甘油三酯含量没有显著性影响(P>0.05).赖氨酸含量为3.25%时,干物质和蛋白质的表观消化率最高,而脂肪消化率的最高值出现在3.68%赖氨酸的饲料组.试验结果还表明,黑鲷幼鱼胃、前肠和中肠的蛋白酶活性变化趋势基本一致.随着饲料中赖氨酸水平的增加而升高(P<0.05),过高的饲料赖氨酸水平则会降低蛋白酶活性,各组间的胃、前肠和中肠的脂肪酶活性先下降后升高(P<0.05),饲料赖氨酸水平对黑鲷幼鱼胃、前肠和中肠的淀粉酶活性没有显著影响(P>0.05).使用曲线模型,根据试验黑鲷幼鱼的增重率同饲料中赖氨酸水平的相关性得出其赖氨酸需要量为3.28%,占饲料蛋白质的8.63%.

Study on Lysine Requirement of Juvenile Black Sea Bream(Sparus macrocephalus)

An 8-week feeding experiment was conducted to investigate the effects of lysine on growth performance, body com-position, digestive ability and determine the quantitative lysine requirement of juvenile black sea bream (Sparus macrocepha-lus). Three hundred and sixty fish with initial body weight of (9.13 ± 0.09) g were randomly divided into 6 treatments with 3 replicates each and 20 fish in each replicate. Six treatments were fed with 6 iso-nitrogenous and iso-energetic diets contai-ning 6 levels of lysine (2.08%, 2.52%, 2.88%, 3.25%, 3.68% and 4.05%). The results showed that, weight gain ratio (WGR) and specific growth rate (SGR) increased with the level of dietary lysine increased to 3.25% from 2.08% (P< 0.05) and both showed a declining tendency thereafter. Feed efficiency (FE) was lower for fish fed with the lower lysine level(2.08% and 2.52%) diets (P<0.05) and it showed no significant differences among other treatments (P>0.05). The protein efficiency ratio (PER) increased significantly with the level of dietary lysine increased to 3.25% from 2.08% (P< 0.05), and thereafter, it remained stable. Survival ratio (SR) and hepatopancreas index (HSI) had no relationship with the level of lysine. The whole body crude protein and crude lipid contents were significantly affected (P<0.05) by dietary ly-sine level, while moisture and ash contents showed no significant differences (P>0.05). Both total essential amino acid and lysine contents in liver obtained the highest values when the fish were fed with 3.68% lysine diet (P<0.05). The content of cholesterol (CHO), alanine transaminase (ALT) and aspartate aminotransferase (AST) in serum showed declining tendency with the increasing lysine level, and all reached the lowest values at 3.68% lysine level, however, no significant difference (P>0.05) was found in serum triacylglycerol (TG). The dry matter apparent digestibility (DMAD), crude protein appar-ent digestibility (CPAD) and fat apparent digestibility (EEAD) reached the highest values when fish were fed with 3.25%, 3.25% and 3.68% lysine diet, respectively. The results showed that the activity of protease in stomach, foregut and midgut increased with increasing lysine level although there was declining for fish fed with the last two lysine levels. The activity of lipase showed the reversed tendency. However, the activity of amylase was not influenced by lysine levels (P>0.05). Anal-ysis of dose (lysine level)-response (weight gain rate) with second order polynomial regression suggested that the lysine re-quirement of juvenile black sea bream was 3.28% of diet or 8.63% of dietary protein (DM basis).