大口黑鲈对饲料中酵母硒的耐受性研究

本试验旨在通过研究酵母硒对大口黑鲈生长性能、血浆生化指标、组织抗氧化指标及肝脏组织结构的影响,评价大口黑鲈对饲料中酵母硒的耐受性。在基础饲料中分别添加0(Y0)、0.5(Y0.5)、2.5(Y2.5)、5.0 mg/kg(Y5.0)(以硒计)酵母硒,其中0.5 mg/kg是硒的最高推荐剂量,2.5和5.0 mg/kg分别是最高推荐剂量(0.5 mg/kg)的5和10倍。基础饲料本底硒含量为0.76 mg/kg。选用初始体重为(12.99±0.01)g大口黑鲈,随机分为4组,每组6个重复,每个重复20尾,试验期为10周。结果表明:Y0组增重率和摄食率最低,同时其饲料系数也最低,均显著低于其余各组(P0.05)。Y0组血浆中碱性磷酸酶活性显著高于其余各组(P0.05)。Y0.5组血浆中高密度脂蛋白胆固醇含量显著高于其余各组(P0.05)。Y2.5组血浆中尿素氮含量显著高于其余各组(P0.05)。Y2.5组、Y5.0组血浆中免疫球蛋白M含量显著高于Y0组、Y0.5组(P0.05)。与Y0组相比,酵母硒的添加显著降低了血浆中丙二醛的含量(P0.05),且显著提高了血浆中谷胱甘肽过氧化物酶的活性(P0.05)。Y5.0组肝脏硒含量显著高于Y0组、Y 0.5组(P0.05),与Y2.5组无显著差异(P0.05)。硒日摄入量和肝脏硒含量呈显著线性相关(P0.05),肝脏硒含量随硒日摄入量的提高呈线性增加。各组大口黑鲈的肝脏都有不同程度的损伤,但添加0.5 mg/kg酵母硒对肝脏损伤有缓减作用。由上述结果可知,饲料中添加0.5 mg/kg酵母硒(总硒含量为1.29 mg/kg)对大口黑鲈具有一定的脂肪代谢促进作用和抗氧化保护功能,且对大口黑鲈是安全的。本试验条件下,综合生长性能、血浆生化指标、组织抗氧化指标及肝脏组织结构,饲料本底硒含量为0.76 mg/kg时,大口黑鲈对饲料中酵母硒的耐受剂量为0.5 mg/kg(以硒计),即为硒的最高推荐剂量,安全系数为1。鱼粉、磷虾粉等动物蛋白质源中含有较高水平的硒元素,因此在高鱼粉水产动物饲料中补充硒要慎重。

Tolerance of Selenium-Yeast in Diets of Largemouth Bass (Micropterus salmoides)

A 10-week growth trail was conducted to evaluate the tolerance of selenium (Se)-yeast in diets of largemouth bass (Micropterus salmoides) by studying the effects of Se-yeast on growth performance, plasma biochemical indices, tissue antioxidant indices and hepatic histology of largemouth bass.Four experimental diets were prepared with Se-yeast supplemental levels at 0 (Y0), 0.5 (Y0.5), 2.5 (Y2.5) and 5.0 mg/kg (calculated in Se) (Y5.0) based on a basal diet, in which 0.5 mg/kg was designed as the maximum recommended level, and the 2.5 and 5.0 mg/kg were 5 and 10 folds of the maximum recommended level, respectively.The background Se content in the basal diet was 0.76 mg/kg.Each diet was fed to 6 replicates with 20 largemouth bass with the initial body weight of (12.99±0.01) g.The results showed as follows: fish in Y0 group showed the lowest weight gain rate, feeding rate and feed conversion ratio, which were significantly lower than those of fish in other groups (P<0.05).Plasma alkaline phosphatase (AKP) activity in Y0 group was significantly higher than that in other groups (P<0.05).The content of plasma low density lipoprotein cholesterol (HDL-C) in Y0.5 group was significantly higher than that in other groups (P<0.05).The content of plasma urea nitrogen (UN) in Y2.5 group was significantly higher than that in other groups (P<0.05).Plasma immunoglobulin M (IgM) content in Y2.5 and Y5.0 groups was significantly higher than that in Y0 and Y0.5 groups (P<0.05).Compared with Y0 group, plasma malondialdehyde (MDA) content was significantly decreased (P<0.05), and plasma glutathione peroxidase (GSH-Px) activity was significantly increased by Se-yeast supplementation (P<0.05).Liver selenium content in Y5.0 group was significantly higher than that in Y0 and Y0.5 groups (P<0.05), but had no significant difference compared with Y2.5 group (P>0.05).Daily selenium intake had a significant linear correlation with liver selenium content (P<0.05), and the liver selenium content showed a linear increase with the daily selenium intake increasing.Different degrees of liver histological damage were observed in all groups, and fish fed diets with 0.5 mg/kg Se-yeast relieved the symptom.The present study shows that the diet with 0.5 mg/kg Se-yeast (total Se content is 1.29 mg/kg) can enhance the lipid metabolism and antioxidant response of largemouth bass, and it is safe for largemouth bass.Growth performance, plasma biochemical indices, tissue antioxidant indices and hepatic histology are considered synthetically, the tolerance dose of Se-yeast in diet with 0.76 mg/kg background Se for largemouth bass is 0.5 mg/kg (calculated in Se), that is the maximum recommended level of Se, and the safety margin is 1.Animal protein sources such as fish meal and krill meal contain high level of Se element, which need to be cautiously considered when exogenic Se sources are used in high fish meal diets for aquatic animals.