Effects Of Stocking Density On Growth,Biochemical And Immune Indexes Of Leiocassis Longirostris Juveniles In Pond Juanyang Mode

The pond Juanyang mode is a new type of intensive aquaculture technology,compared with the traditional pond free-range aquaculture mode,the Juanyang mode converts fish from free-range aquaculture to Juanyang,which greatly reduces the consumption of water resources.The Juanyang mode has the advantages of energy saving and emission reduction,ecological the advantages of environmental protection,high production efficiency and healthy and safe aquatic product quality.Stocking density is an important stress factor affecting the growth of fish,Unsuitable density will make fish in a state of stress for a long time,which will negatively affect their growth,physiology and immunity.This study took Longsnout catfish(Leiocassis longirostris)as the research object.The initial body weight of the experimental fish was 16.39±4.22 g,and the initial body length was 9.94±0.78 cm.The low density group was set at 1500 tails/circle(LSD,1.23±0.07 kg/m~3),3000 tails/circle(MSD,2.44±0.13 kg/m~3)in medium density group,4500 tails/circle(HSD,3.54±0.20 kg/m~3)in high density group,3 replicates for each density group,breeded time was 90 d,the differences in the growth,serum biochemistry,antioxidant enzyme activity and non-specific immunity of the juvenile of Longsnout catfish s of the three densities were compared.In order to explore the suitable stocking density for the cultivation of Longsnout catfish.The main results are as follows:1、The terminal densities of LSD,MSD,and HSD groups were 5.40±0.14 kg/m~3,9.59±0.11 kg/m~3,and 13.71±0.88 kg/m~3,respectively,there was no significant difference in body weight and body length among the density groups at the early stage of breeding(45 d),the body weight and body length of each density group decreased significantly(P<0.05)with the increase of the density in the late breeding period(60～90 d).In the early breeding period(0～15 d),the Weight gain rate(WGR)of the HSD group was significantly greater than that of the LSD group,in the mid-breeding period(15-45 d),the WGR of the LSD group was significantly greater than that of the HSD group(P<0.05),and in the late-breeding period(60-90 d),the WGR of each density group had no significant difference.All density groups grew slowly,Specific growth rate(SGR)and WGR had similar trends.The fluctuation of Condition factor(CF)throughout the breeding stage was small,and there was no significant difference between the density groups,Viscera weight index(VSI)and Hepatosmatic index(HSI)were all showed an increasing trend with time,indicating that the stocking density had little effect on the body fatness and energy storage status of the juveniles of Longsnout catfish.2、The high stocking density had no effect on the blood glucose(Glu)content of the juveniles,while the triglyceride(TG)and cholesterol(CHO)contents slightly increased with the breeding density,And the total protein(TP)and albumin(TP)increased significantly with the increase of breeding density(P<0.05);Stocking density had no significant effect on aspartate aminotransferase(AST)、alanine aminotransferase(ALT)and alkaline phosphatase(ALP).3、Stocking density had little effect on the activity of two antioxidant enzymes in serum,namely superoxide dismutase(SOD)and catalase(CAT),but had a significant effect on the content of lipid peroxidation product malondialdehyde(MDA).The content of MDA increased significantly with the increase of the breeding density in the late breeding period(P<0.05),indicating that the high density produced crowding stress on the juveniles of Longsnout catfish,resulting in the increase of the content of reactive oxygen radicals in the body and the enhancement of lipid peroxidation.This resulted in a certain degree of oxidative damage,the stocking density had no correlation with the activity of serum lysozyme(LZM),while the contents of complement 3(C3)and complement 4(C4)increased with the increase of the stocking density,indicating that under high density conditions,the complement system is activated in juvenile fishes to enhance immunity against crowding stress,To sum up,in the early and mid-term of the experiment,the stocking density had no effect on the growth of the juveniles,but after reaching a certain density from 60 d,the growth was inhibited,and has certain negative effects on biochemical indicators,antioxidant properties and non-specific immunity,Therefore,it is recommended that in the actual production process of Juanyang the juveniles of Longsnout catfish,a grading method can be adopted,The stocking density of juvenile fish can be as high as 4500 tails/circle,and when the weight reaches about 50 g,grading should be carried out,and the density should be controlled at 2000～3000tails/circle.