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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%。
A total of 360 juvenile Sparus macrocephalus juveniles with initial body weight (9.13 ± 0.09 g) were randomly divided into 6 groups with 3 replicates in each group and 20 replicates per group. The measured lysine levels were respectively fed at 2.08% , 2.52%, 2.88%, 3.25%, 3.68% and 4.05% of isonitrogenic equivalent diets. The experimental period was 8 weeks. The effects of dietary lysine on the growth performance, body composition and digestibility of black sea bream were observed, and the appropriate lysine requirement was determined. The results showed that when the lysine level in feed increased from 2.08% to 3.25%, the weight gain rate and specific growth rate of black sea bream increased with the increase of dietary lysine level (P <0.05), then appeared Decreasing trend. The feed efficiency of low lysine group (2.08% and 2.52%) was lower than that of other groups (P <0.05), but there was no significant difference between other groups (P> 0.05). Feed lysine level increased from 2.08% to 3.25%, protein deposition rate was significantly increased (P <0.05), then stabilized. Survival rate and liver body ratio and lysine level has nothing to do. The protein content of whole fish increased with the increase of dietary lysine, while the fat content showed a downward trend. There was no significant difference between the groups in ash and water content (P> 0.05). The liver total essential amino acids and lysine contents increased with increasing dietary lysine levels, but both indicators were significantly lower (P <0.05) at the highest lysine supplement level. Serum cholesterol, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) activity decreased with increasing dietary lysine content, with the lowest lysine content reaching 3.68%, while serum triglyceride content No significant effect (P> 0.05). The apparent digestibilities of dry matter and protein were the highest when lysine content was 3.25%, while the highest value of fat digestibility appeared in 3.68% lysine feed group. The results also showed that the changes of protease activity in the stomach, foregut and midgut of juvenile black sea bream were basically the same, with the increase of dietary lysine (P <0.05), too high feed lysine (P <0.05). The dietary lysine level decreased the activity of lipase in the stomach, foregut and midgut of the black seabream juveniles Amylase activity had no significant effect (P> 0.05). Using the curve model, the lysine requirement was 3.28%, accounting for 8.63% of the dietary protein, based on the correlation between the weight gain rate of juvenile black sea bream and the feed lysine level.