不同盐度对珍珠龙胆石斑鱼幼鱼生长、消化酶活性和非特异性免疫的影响

Effects of salinity on growth performance, digestive enzymes, and nonspecific immunity in juvenile hybrid grouper (Epinephelus fuscoguttatus♀× E. lanceolatus♂)

关键词:  珍珠龙胆石斑鱼  盐度  生长性能  消化酶  非特异性免疫

Key words:  Epinephelus fuscoguttatus♀×E. lanceolatus♂  Salinity  Growth performance  Digestive enzymes  Nonspecific Immunity

摘要:

本研究以珍珠龙胆石斑鱼(Epinephelus fuscoguttatus♀×E. lanceolatus♂)幼鱼[(29.99±2.60) g]为研究对象，旨在探究不同盐度对珍珠龙胆石斑鱼幼鱼生长性能、机体化学组成、消化能力、抗氧化能力及血清部分生化指标的影响。实验设计6个盐度梯度，分别为10、15、20、25、30和35，分别命名为S1、S2、S3、S4、S5和S6，每个实验组3个重复，实验期为28 d。结果显示，增重率(WGR)和饲料效率(FE)随盐度升高均呈先升高后降低的趋势，且最大值均在S4组，显著高于S1和S6组(P<0.05)，存活率在不同实验组间无显著性差异(P>0.05)。全鱼和肌肉粗脂肪含量呈现同WGR相似的变化趋势。肠道脂肪酶和胰蛋白酶活性在S3和S4组处于较高水平，显著高于其他各组(P<0.05)。S1和S6组的肝脏超氧化物歧化酶(SOD)、总抗氧化能力(T-AOC)和过氧化氢酶(CAT)活性显著高于其他各实验组(P<0.05)。丙二醛(MDA)含量在S3和S4组较低，显著低于其他4个实验组(P<0.05)。随盐度升高，血清中谷草转氨酶(AST)、谷丙转氨酶(ALT)、碱性磷酸酶(AKP)和乳酸脱氢酶(LDH)活性均呈先降低后升高的趋势，在S3和S4组处于较低水平，且显著低于S1和S6组(P<0.05)。以WGR和FE作为评价指标，经二次回归模型分析得出，珍珠龙胆石斑鱼幼鱼最适盐度分别为22.18和23.16。综上所述，适宜的盐度(20~25)能促进珍珠龙胆石斑鱼幼鱼的生长，提高肠道消化能力，同时，鱼体的非特异性免疫系统能够响应不同的盐度条件，保持机体健康。

Abstract:

In recent years, many studies on the effects of salinity on fish growth performance have been performed. A series of research results confirmed that appropriate salinity could guarantee healthy fish growth, while under extremely high or low salinity, the fish growth would be inhibited. Therefore, salinity is one of the critical factors ensuring aquaculture success. However, most previous studies only focused on fish growth and survival, without systematically analyzing the physiological and biochemical indicators or performing regression analysis of optimal salinity, especially for the hybrid grouper (Epinephelus fuscoguttatus♀×E. lanceolatus♂). A 28-day experiment was conducted to evaluate the effects of different salinities on growth performance, body composition, digestive enzyme activities, antioxidant indices, and serum biochemical indices of the juvenile hybrid grouper [initial mean weight of (29.99±2.60) g]. This study used six salinity levels of 10, 15, 20, 25, 30, and 35, named S1 (control), S2, S3, S4, S5, and S6, respectively. During the experiment, the water temperature was kept at 25–28 ℃, DO≥6 mg/L, pH 8–9, and the contents of ammonia and nitrite nitrogen were both lower than 0.1 mg/L. Firstly, the results showed that different salinity levels had different impacts on the juvenile hybrid grouper growth performance. The weight growth rate (WGR) and special growth rate (SGR) first increased and then decreased with the rise in salinity and peaked in the S4 group, which were significantly higher than those of the S1 and S6 groups (P<0.05). The feed efficiency (FE) showed a similar tendency to WGR and SGR (P<0.05). Moreover, the survival rate had no significant difference among all groups (P>0.05). The quadratic regression model analysis based on WGR and FE indicated that the optimal salinities were 22.18 and 23.16. Secondly, the whole fish crude lipid content in the S4 group (10.86%) was significantly higher than in the S1 (9.30%), S2 (9.62%), S3 (9.79%), and S6 (9.22%) groups (P<0.05). The muscle crude lipid content in the S3 (2.84%) and S4 (2.95%) groups were significantly higher than that of the S1 (2.23%), S2 (2.34%), S5 (2.44%), and S6 (2.19%) groups (P<0.05). The whole fish crude protein content peaked in the S3 group (65.24%), which was significantly higher than that of the S5 group (63.74%) (P<0.05), with no significant differences observed among other groups (P>0.05). The muscle crude protein content and the whole fish and muscle moisture and ash had no significant differences among all groups (P>0.05). Thirdly, juvenile hybrid grouper´s intestinal lipase and trypsin activities in the S3 and S4 groups were significantly higher than in other groups (P<0.05). In addition, the intestinal amylase activity was kept at 0.19–0.21 U/(mg prot) among all groups, with no significant differences (P>0.05). Fourthly, salinity changes greatly impacted the antioxidant capacity of the juvenile hybrid grouper liver. The activities of the liver superoxide dismutase (SOD), total antioxidant capacity (T-AOC), and catalase (CAT) were significantly higher in the S1 and S6 groups than in other groups (P<0.05). The liver malondialdehyde (MDA) content in the S3 and S4 groups were significantly lower than that of other groups (P<0.05). Fifthly, lower activity levels of the aspartate aminotransferase (AST), cereal third transaminase (ALT), and alkaline phosphatase (AKP) in serum were found in the S3 and S4 groups, which were significantly lower than those of the S1 and S6 groups (P<0.05). Moreover, the ALT activity in the S6 group was significantly lower than in the S1 group (P<0.05). The lower activity level of lactate dehydrogenase (LDH) in serum was also found in the S3 and S4 groups, which were significantly lower than in other groups (P<0.05). In summary, these results indicated that optimal salinity (20–25 mmol/L) could improve the juvenile hybrid grouper growth, while increasing the activities of digestive enzymes, antioxidant properties, and nonspecific immunity capacity, protecting the fish health. At the same time, the quadratic regression model analysis based on WGR and FE indicated that the optimal salinity for juvenile hybrid grouper is between 22.18 and 23.16.