| In recent years,with the rapid development of the aquaculture industry,the problem of shortage of aquatic feed resources has become increasingly serious.As fish meal protein is the main protein source in sturgeon farming feed,its raw material prices have also been continuously soaring,which inevitably increases the cost of artificial sturgeon farming.Therefore,finding high-quality and inexpensive alternative protein sources has become the core issue of the sturgeon farming industry.This study focuses on hybrid sturgeon juveniles,using rapeseed meal to replace a fish meal to evaluate its effects on growth performance,whole-body composition,whole-body amino acids,liver antioxidant indicators,blood biochemical indicators,digestive enzymes,intestinal morphology,and gene expression levels,to provide a basis for rapeseed meal in sturgeon feed formulation.A total of 450 hybrid sturgeon juveniles with similar weights were randomly allocated to five treatment groups,with three replicates per group and 30 fish per tank.Rapeseed meal was used to replace fish meal at 0%,25%,50%,75%,and 100%,respectively,and fed continuously for 12 weeks.The experimental results are as follows:(1)The effects of rapeseed meal replacing fish meal on the growth performance and expression levels of growth genes of sturgeonWith the increase in the proportion of rapeseed meal replacement,final body weight,weight gain rate,and survival rate showed a decreasing trend.When the proportion of rapeseed meal replacing fish meal exceeded 75%,final body weight,and weight gain rate were significantly lower than those in the control group(P < 0.05),and the feed conversion rate was significantly higher than that in the control group(P < 0.05).When the proportion of rapeseed meal replacing fish meal exceeded 50%,the specific growth rate was significantly lower than that in the control group(P < 0.05).With the increase in the level of rapeseed meal replacing fishmeal,the expression levels of GH,and IGF-1 genes in the intestine of sturgeon showed a significant decrease(P <0.05),reaching their lowest levels when the substitution level reached 100%,which was significantly lower than that of the control group(P < 0.05).Therefore,it can be concluded that when the proportion of rapeseed meal replacing fish meal is no higher than 50%,there is no significant adverse effect on the growth performance of hybrid sturgeon.(2)The effects of rapeseed meal replacing fish meal on the whole-body amino acids of sturgeonRapeseed meal replacement had no significant effect on the moisture,dry matter,and crude fat content of sturgeon body composition(P > 0.05).With the increase in rapeseed meal replacement proportion,the crude protein and crude ash content showed a decreasing trend.The whole fish Thr,Met,and total amino acid content of sturgeon tended to increase as the proportion of feed fishmeal replaced by rapeseed meal increased(P < 0.05)and reached a maximum when the proportion of feed fishmeal replaced by rapeseed meal was 100%;when the proportion of feed fishmeal replaced by rapeseed meal exceeded 25%,the whole fish Leu and Lys content of sturgeon tended to increase(P < 0.05)and reached a maximum when the proportion of feed fishmeal replaced by rapeseed meal increased to 100% and was significantly greater than the other test groups(P < 0.05).The maximum value was reached when the percentage of substitution was increased to 100% and was significantly greater than the other test groups(P < 0.05).When the proportion of rapeseed meal substituted for fishmeal exceeded 50%,the levels of Val and Ile in whole sturgeon increased(P < 0.05),with Val and Ile levels significantly greater than in the other groups at 100% substitution(P < 0.05),but the levels of His and Arg in all groups were not significantly different from the control group(P < 0.05).However,the levels of His and Arg in each test group were not significantly different(P < 0.05)compared to the control group.The levels of Glu,Ala,Tyr,and Pro in whole sturgeon increased with the proportion of fish meal replaced by rapeseed meal(P < 0.05).In particular,the whole fish Glu content of sturgeon reached a maximum when the substitution ratio increased to 50% and was significantly higher than the control group(P < 0.05);when the substitution ratio increased to 100%,the whole fish Ala,Tyr,and Pro content of sturgeon reached a maximum and was significantly higher than the control(P < 0.05).(3)Effects of replacing fish meal with rapeseed meal on antioxidant capacity,non-specific immunity,and serum biochemical parameters in the liver of sturgeonWhen the proportion of fish meal replaced by rapeseed meal increased to 75%,the sturgeon liver superoxide dismutase and malondialdehyde activities reached their highest values and the malondialdehyde activity was significantly higher than that of the control group(P < 0.05);the lysozyme activities in the pyloric cecum,duodenum,and valve intestine of sturgeon tended to decrease as the proportion of fish meal replaced by rapeseed meal in the diet increased(P > 0.05).The lysozyme activities in the pyloric cecum,duodenum,and valve intestine were significantly lower(P < 0.05)than those in the control group when the substitution ratio was increased to 100%;there was no significant change in the lysozyme activities in the stomach of sturgeon(P > 0.05);the levels of glucose,total protein,and albumin in blood tended to increase(P < 0.05)as the proportion of fish meal replaced by rapeseed meal increased,while the substitution The levels of alanine transaminase and aspartate transaminase in blood were significantly higher than those in the other test groups at 25% and 100%(P < 0.05),while the levels of albumin in all test groups were significantly higher than those in the control group(P < 0.05),while the levels of triglyceride in all test groups were significantly lower than those in the control group(P < 0.05),and the levels of cholesterol in blood did not differ significantly between the groups(P > 0.05).(4)Effect of rapeseed meal replacing fishmeal on the morphological structure of the duodenum in sturgeonWith the increase in the proportion of rapeseed meal replacing fishmeal,the thickness of the mucosa and submucosa in the duodenum of sturgeon showed a significant decreasing trend(P <0.05),reaching its minimum value when the substitution ratio reached 100%.When the proportion of rapeseed meal replacing fishmeal exceeded 25%,the villus width in the duodenum of the sturgeon showed a significant decreasing trend(P < 0.05).In contrast,when the proportion of rapeseed meal replacing fishmeal reached 25%,the villus height in the duodenum of sturgeon was significantly higher than that of the control group(P < 0.05),when the proportion of rapeseed meal replacing fishmeal reached 100%,the villus height in the duodenum of sturgeon was significantly lower than that of the control group.(5)Effect of rapeseed meal replacing fishmeal on the expression levels of immune-related genes in sturgeonThe expression levels of IL1β,IL-6,IL-8,and TNF-α genes in the gut increased significantly(P < 0.05)as the level of rapeseed meal substitution for fishmeal increased,and reached the highest value when the substitution level rose to 100%,significantly higher than the control(P <0.05).The expression level of the IL-10 gene decreased significantly(P < 0.05)as the level of fishmeal substitution by rapeseed meal increased,with the expression of the IL-10 gene reaching the lowest value when the substitution level increased to 100%,which was significantly lower than that of the control group(P < 0.05).The expression levels of TLR2,NF-κB and My D88 genes in the intestine increased significantly(P < 0.05)as the level of rapeseed meal substitution for fishmeal increased,and reached the highest value when the substitution level increased to 100%,which was significantly higher than the control group(P < 0.05).The expression levels of TLR1 genes decreased significantly(P < 0.05)as the level of rapeseed meal substitution for fishmeal increased,with the expression of TLR1 genes reaching the lowest value when the substitution level increased to 100%,significantly lower than the control(P < 0.05). |
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