The Influence Of Stocking Density On The Growth Performance, Physiological And Biochemical Indices And Nonspecific Immunity Of Juvenile Russian Sturgeon In Flowing Water Cultivation

Nowadays, some countries in Europe. Asia, and North America have developed the techniques for sturgeon artificial breeding according to the conservation acts. Russian sturgeon (Acipenser gueldenstaedti) is one of the rare and valuable fish species, which has become one of the popular sturgeon culture species in China. It has been demonstrated that people tend to get more benefit by increasing stocking density, which may suppress fish growth due to the decreasing of food consumption efficiency and the alteration in metabolic rate induced by crowding stress associated with stocking densities. This study was undertaken to investigate the influence of different stocking density on the growth performance of juvenile Russian sturgeon. Three triplicate groups of juveniles(initial body weight(29.7±1.32 g) are reared in nine square concrete ponds(4.4±4.4x0.45 m3) at three stocking densities(2.5 kg/m3(SD1)、 3.6 kg/m3(SD2)、4.7 kg/m3(SD3) for 90 days. The result is as follows:1.The weight gain (GBW), length gain (GBL), specific growth rate (SGR) and food conversion ratio (FCR) of the fishes in low density(SD1) are (362.01±15.87、 55.88±4.77、1.79±0.03、114.95±4.52), respectively, which are significant higher than those in high density (SD3)(272.30±2.74、46.34±6.22、1.53±0.02.94.49±1.96) (P <0.05)。the mortality and greater variation in size and growth of the juvenile fishes in SD3 are significant higher than those in SD1 (P<0.05); Meantime, the protein and fat content decreased while the moisture and ash content increased along with the density increasing, but there is no significant difference (P>0.05). These results suggested that high density have a significant negative impact on the growth performance of juvenile Russian sturgeon, and the growth suppression caused by high stocking density might be associated with the crowding stress and reductions in both food consumption and food conversion efficiency.2.Long period of chronic stress from high stocking density has a great influence in the physiological and biochemical indices of Russian sturgeon. The hemoglobin content is significantly and positively correlated with the stocking density. Leukocyte content of different stocking density Russian sturgeon have significant differences. The white blood cell count of juvenile Russian sturgeon in group SD3 is significantly higher than those in group SD1. SD2 (P<0.05), The results suggesting that the long-term high-density culture of the Russian sturgeon can lead to physical and pathological damage of body. By the end of the experiment,The blood-sugar levels all offered upgrade firstly than descending latter tendency, the content of SD1 is the lowest. Total cholesterol and total protein have no significantly changes (P>0.05). At the end of the experiment. The triglyceride content of juvenile blood in group SD3 is significantly higher than SD1 (P<0.05),and there is no significant difference between group SD1 and SD2. These survey results indicate that the order of energy utilization in Russian sturgeon followed by blood sugar, serum protein and blood lipids. The cortisol levels increased dramatically when the density reach 12.12kg/m3,which can promote gluconeogenesis, inhibit the growth of Russian sturgeon.3.The SOD activity in high stocking density is significantly lower than in low stocking density (P< 0.05). which indicates that the high stocking density can break the balance of the body’s antioxidant system and inhibit the antioxidant function, even reduce the ability of oxygen free radical eliminating. In the meantime, the MDA content in group SD3 is significantly higher than group SD1 and SD2 (P<0.05). which heads from the enhancement of lipid peroxidation. The crowding stress resulting from the excessive stocking density can break the balance of free radical unstable state and affect normal physiological state. The spleen coefficient in group SD3 is significantly lower than in group SD1、SD2,lysozyme activity and C3 complement level has the same changing trend, which indicates that chronic crowding stress can cause spleen damage and immune function incapacitated.