| Silkworm pupae,the by-product of silk reeling,is a high-quality protein source with sufficient sources and low price.However,its low processing and utilization rate result in huge waste of resources and environmental pollution.Largemouth bass(Micropterus salmoides)is an important economically farmed fish in China.However,due to its carnivorous characteristics,the breeding cost of largemouth bass is rising as the price of fish meal continues to increase.In this study,largemouth bass was used as the research object to explore the effects of fish meal replacement by fermented silkworm pupae on its growth performance,feed utilization and fish body composition,and the cost was analyzed.In addition,the relevant influencing mechanisms were explored from the perspectives of molecular level and intestinal microorganism.The main research results are as follows:(1)According to the basic feed of largemouth bass and its nutritional requirements,the fermentation conditions of silkworm pupae in silkworm reels were retroactively optimized to explore the potential of silkworm pupae as a substitute for nitrogen source of fish meal in the feed of largemouth bass,and the nutritional value of the prepared feed was comprehensively evaluated.The results showed that when fish meal was directly replaced by silkworm pupae meal,the content of crude protein in the feed was limited and the content of crude fat in the feed was high,which could easily cause fat deposition in the fish body and impede the nutritional requirements of largemouth bass.Therefore,silkworm pupae should be processed.Candida albicans was used to ferment silkworm pupae(inoculation amount was 2%).Compared with untreated silkworm pupae,the crude protein content of silkworm pupae after fermentation treatment was increased by 13.93%(p<0.05),the crude ash content was decreased by 83.32%(p<0.05),the total protein amino acid content was increased by 2.55%,the protein solubility of the product was increased by 6.01times(p<0.05),and the peptide yield was increased by 13.41 times(p<0.05).The macromolecular proteins with molecular weight above 15 k Da were effectively degraded.After fermentation,the scavenging activity of DPPH free radical,the scavenging activity of superoxide free radical and the reducing power of silkworm pupa protein hydrolysate were increased by 12.54%,93.38% and 51.28%,respectively.In addition,compared with enzymatic hydrolysis treatment,fermentation can effectively improve the sensory odor of silkworm pupae.Isonitrogenous and isoenergetic experimental diets(protein: 45.97%,energy: 16.91±0.02 kcal/kg)were prepared replacing fish meal with fermented silkworm pupae meal,and enhancing the nutritional requirements of largemouth bass.In conclusion,fermented silkworm pupae have the potential to substitute fish meal in largemouth bass diet.Fermented silkworm pupae can replace fish meal feed to meet the application requirements of largemouth bass,and can be used for subsequent nutrition experiments.(2)Evaluation of feeding largemouth bass with fermented silkworm pupae meal instead of fish meal.The effects of fermented silkworm pupae meal on the growth,feed utilization and fish body composition of largemouth bass were investigated,and the economy of the alternative scheme was analyzed.The results showed that the survival rates of the experimental groups were 100% after feeding the largemouth bass for 70 days,and the specific growth rate of the 30% fermented silkworm pupae replacement group(G3)increased by 8.6%,the feed use efficiency increased by 26.22%(p<0.05),and the viscera body ratio decreased by 22.20%(p<0.05),which indicated that it could promote the growth of largemouth bass and enhance its edibility.The crude protein content of fish muscle was increased by 16.66%(p<0.01),the crude lipid content was decreased by 82.86%(p<0.01),the umami amino acid content was increased by 1.05 times,and the flavor amino acid content was increased by 1.06 times,indicating a significant effect by the fish body composition(p<0.05).Determining that the replacement proportion of fish meal to fermented silkworm pupae meal in feed is 30%,indicating the best alternative level,the production cost of largemouth bass could be reduced by about 1/3.In conclusion,the substitution of 30% fermented silkworm pupae for feed could effectively promote the growth and enhance the edibility of largemouth bass.In addition,the replacement scheme had a good technical and economic efficiency.(3)To study the mechanism of replacing fish meal with fermented silkworm pupae on the growth and health of largemouth bass at molecular level.The expressions of lipid-metabolism-related genes(CPT-1,LPL,and HL),hormone-regulatory genes(GH,IGF-1,and LEP-A),and immune-related genes(TLRs and ILs)in the whole brain and liver tissues of largemouth bass were detected by real time q PCR.The results showed that compared with the control group,the replacement of 30% fermented silkworm pupae powder could significantly up-regulate the lipid metabolism-related genes LPL and HL(p<0.01)to inhibit lipid deposition of largemouth bass.The replacement of 30% fermented silkworm pupae meal significantly increased GH(p<0.01)and LEP(p<0.01)to promote the catabolism of body fat in largemouth bass.The replacement of 30% fermented silkworm pupae powder could up-regulate the immune-related genes TLRs and ILs(p<0.01),thus enhancing the body immunity of fish.In conclusion,the replacement of 30% fermented silkworm pupae powder in the diet can significantly affect the lipid metabolism,hormone regulation and expression of immune-related genes,and regulate the growth and development of largemouth bass and the body immunity.(4)To explore the mechanism of replacing fish meal with fermented silkworm pupae on the growth and health of largemouth bass from the perspective of intestinal microorganism.16 S r DNA Amplicon Sequencing technology was used to amplify the V3-V4 variable region of total DNA of intestinal bacteria of largemouth bass in the control group and 30% fermented silkworm pupae replacement group,respectively.The results showed that replacing fish meal with 30% fermented silkworm pupae did not change the dominant flora of largemouth bass,but the species abundance of Proteobacteria decreased by 68.14%,the ratio of Firmicutes to Bacteroidetes decreased by 1.24 times,and the species abundance of Actinobacteria increased by 83.81% in G3 group.Among the intestinal microflora of largemouth bass in G3 group,the species abundance of 3 species was significantly up-regulated(p<0.05),and 2 species was significantly down-regulated(p<0.05),however,there was no difference in the majority(p＞0.05).The diversity of intestinal microflora of largemouth bass was increased by 1.31 times,and the unique functions were enriched(p<0.05).In conclusion,the replacement of fermented silkworm pupae can alter the abundance and species diversity of dominant microflora in the intestinal tract of largemouth bass,and regulate the absorption and utilization of dietary nutrients by largemouth bass.In conclusion,largemouth bass was employed as the research subject in this study and six isonitrogen-isoenergy feeds were prepared.Fish meal was replaced by fermented silkworm pupae at different levels,and the optimal replacement level was determined by the feeding effect study.In addition,combined with the analysis of the expression of genes related to growth,metabolism and immunization,and the abundance and diversity of intestinal flora of largemouth bass,the mechanism of the optimal substitute level feed of fermented silkworm pupae meal on largemouth bass was explored.This study provides information for the development of fish meal substitute protein source in largemouth bass feed and the saving of aquaculture costs.Moreover,the resource utilization of silkworm pupae and the diversification of sericulture industry could be promoted. |
PDF Full Text Request