| Black soldier fly(Hermetia illucens),insects of the Dipteraas,originating in the Americas,is widely distributed in the tropics and subtropics.Black soldier fly is one of the most potential feed source of insects because of its short growth cycle,FASt reproduction speed and high nutritional value.The research on it mainly focus on the utilization of protein resources.Only few studies focuse on the application of its oil sources.Black soldier fly larvae have a high lipid content and its fatty acid is rich in lauric acid.Studies have pointed out that lauric acid,as an energy fatty acid,can be rapidly oxidized in the body and keep the important effect on lipid metabolism,inflammation and other aspects.In addition,black soldier fly oil also contains more essential fatty acids including lots of linoleic acid(LA)and a little of linolenic acid(LNA),which are necessary for the growth and development of freshwater fish.However,there are few studies on black soldier fly oil as feed material in aquatic animals.Therefore,this research carried out a series of experiments,from black soldier fly oil extraction,oil nutritional ingredient optimization and the evaluation of black soldier fly oil as feed source in aquatic animals in order to comprehensive analysis the feasibility of black soldier fly oil as a new aquatic feed oil source and to provide reference for the development of functional aquatic feed with black soldier fly oil as feed resource.Experiment 1.Extraction and physicochemical property analysis of black soldier fly oilTo evaluate the effect of extraction indexes(reaction time,temperature,the ratio of organic solvents to larvae powder)on the crude lipid extraction content of black soldier fly.This experiment was done with single factor and orthogonal experiment.Then the physical and chemical properties of oil extracted by extraction method and pressing method were compared.It indicated that when the larvae powder to organic solvents=1(g):10(ml),and the reaction temperature was maintained at 50?for 5 hours,its extraction rate could as high as 24.59%.After analyzing of its physical and chemical properties,(1)it indicated that the extracted colour of black soldier fly oil was faint yellow or pale yellow;(2)The acid value,peroxide value,iodine value,saponification value,moisture and unsaponifiable matter between oils separated by squeezing method and extraction method were no significant differences in each other;(3)Then the acid value and peroxide value of oil separated by this two methods were lower than the standard of feed lard,fish oil and soybean oil,so it indicated that black soldier fly oil was a kind of potential feed oil resource.Experiment 2:The study of improving the nutritional value of black soldier fly larvae oil by Schizochytrium residueIn order to improve the nutritional value of black soldier fly oil,larvae(the initial weight of 12.74 mg)were fed on substrates containing 10%,20%,30%and 40%algal residue which had a high content of highly unsaturated fatty acids(HUFA).The breeding period was completed(9 days)until the final body weight of larvae in the algal residue free group was100 mg.After 9 days,(1)the final body weight,body length,crude protein and crude lipid content have no significance in 10%algal residue group and no algal residue group;(2)When the supplemental level of algal residue was higher than 20%,the growth indexes,crude protein and crude lipid of larvae were significantly lower than no algal residue group(P<0.05);(3)The levels of eicosapentaenoic acid(EPA),docosahexenoic Acid(DHA)and n-3 polyunsaturated fatty acids(PUFA)in the larvae fed on algal residue were significantly higher than those in the larvae fed on no algal residue(P<0.05).In conclusion,when 10%algal residue was added to the substrate of black soldier larvae,the larvae had a good growth and the nutritional value of oil could be improved.Experiment 3.Comparison of effects of black soldier fly oil,yellow mealworm oil and silkworm pupa oil on growth and health of juvenile mirror carpFour isonitrogenous and isolipidic diets were prepared in which black soldier fly oil,yellow mealworm oil,silkworm oil and mixed insect oil(three oils ratio 1:1:1)were used as the single oil source respectively.Then three repetitions of each diet(BSFO,SWPO,YMO,MIXO)were given to juvenile mirror carp(13.98±0.01 g)for 59 days.(1)The results indicated that the growth and feed utilization of fish fed with BSFO and MIXO diets were significantly better than the fish fed the other two insect oil diets(P<0.05);(2)Intra-peritoneal fat index(IFI)and adipocyte size in intra-peritoneal fat tissue decreased in the fish fed with BSFO and MIXO compared to fish fed the SWPO and YMO diets(P<0.05).Relative gene expression of fatty acid synthase(FAS)significantly decreased,while peroxisome proliferator-activated receptor-?(PPAR-?)significantly increased in intra-peritoneal fat tissue of fish fed with BSFO and MIXO diets compared with mirror carp fed with SWPO and YMO diets(P<0.05);(3)The activity and transcription of total superoxide dismutase(SOD)significantly increased in the liver of fish fed with BSFO and MIXO than fish fed with SWPO and YMO diets(P<0.05);(4)The content of hepatic maleic dialdehyde(MDA)significantly decreased,while serum globulin(GLO)significantly increased in fish fed with BSFO and MIXO than fish fed with SWPO and YMO diets(P<0.05).Fish fed with SWPO diet significantly up-regulated the hepatic expression of pro-inflammatory cytokine interleukin-1?(IL-1?)and tumor necrosis factor-?(TNF-?)than fish fed with BSFO,YMO or MIXO diets(P<0.05).Overall,compared to others insect oils source(yellow mealworm oil and silkworm oil),inclusion of black soldier fly oil or the combination of the three oils(MIXO)in the diets positively influence growth performance,lipid metabolism of intra-peritoneal fat,liver antioxidant capacity and inflammatory response of juvenile mirror carp.Experiment 4:Influence of dietary black soldier fly oil under different lipid levels on growth performance,body composition and lipid metabolism of juvenile mirror carpA 8-week feeding trial was conducted by two-way Anova with using four isonitrogenous(32.0%crude protein)diets containing 6%lipid(CT),6%lipid+25 g kg-1black soldier fly oil(CT+BSFO),9%lipid(HL)and 9%lipid+25 g kg-1 black soldier fly oil(HL+BSFO).(1)The growth performance and feed utilization capacity of fish at different lipid levels were not affected by the addition of black soldier fly oil,and there was no significant difference in the related indexes between black soldier fly oil groups(CT+BSFO group,HL+BSFO group)and the other two groups(CT,HL group)(P<0.05);(2)The IFI and adipocyte size in CT+BSFO group were significantly smaller than those in CT group(P<0.05).In intra-peritoneal fat tissue,the m RNA concentration of PPAR-?gene in the CT+BSFO group was significantly higher than that in the CT group(P<0.05).In the hepatopancreas,the expression levels of CT+BSFO and HL+BSFO groups were significantly higher than those in CT and HL groups(P<0.05).Hepatopancreas crude lipid content in CT+BSFO group was significantly lower than that in CT group,but there was no significant difference between HL+BSFO group and HL group;(3)Muscle docosahexaenoic acid(DHA)content was influenced by lipid level,oil source and interaction.Dietary DHA content decreased with the increase of lipid level,and DHA content increased with the addition of black soldier fly oil(P<0.05).In conclusion,supplementation of 25 g kg-1 black soldier fly oil in diets with different lipid levels can regulate lipid metabolism by promoting lipolysis and had no negative effect on growth performance.However,the regulation effect of black soldier fly oil on lipid metabolism in high lipid diet was not as obvious as that in low lipid diet.In addition,black soldier fly oil could increase the content of n-3 HUFA and optimize the nutritional composition of muscle in both lipid levels diets.Experiment 5:Effects of dietary black soldier fly oil enriched with n-3 HUFA on growth,health state of juvenile mirror carpExperiment 5.1:Effects of dietary black soldier fly oil enriched with n-3 HUFA replacing soybean oil on growth and health state of juvenile mirror carpIn the present study,we aimed to assess the effect of dietary black soldier fly oil enriched with n-3 HUFA(n-3 HUFA content was 13.2%,the larvae were fed with 10%schistochytrium residue)on growth performance,lipid metabolism,inflammation and related gene expression in juvenile mirror carp.Five isonitrogenous and isolipid diets were prepared by replacing soybean oil with black soldier fly oil enriched with n-3 HUFA 0%(0 g kg-1),25%(6.25 g kg-1),50%(12.5 g kg-1),75%(18.75 g kg-1)and 100%(25 g kg-1),respectively.Juvenile mirror carp(10.05±0.05 g)were fed the diets for 8 weeks.The results indicated that(1)a replacement level at 50%or above(12.5-25 g kg-1)led to the increase in growth performance and feed utilization capacity of fish and(2)a decreased in IFI and adipocyte size,accompanied by relevant changes in gene expression(P<0.05);(3)The same replacement level also improved the characteristics of serum biochemical indexes of juvenile fish,and significantly increased the contents of total protein(TP),GLO and lysozyme(LZM)(P<0.05).Gene expression results of the liver and kidney indicates a less inflammatory state in fish fed more than a 50%replacement of soybean oil with black soldier fly oil(P<0.05).Overall,this study showed that a 50-100%replacement of soybean oil with this n-3HUFA enriched black soldier fly oil positively influences the performance and health status of juvenile mirror carp.Experiment 5.2:Comparative study of common and n-3 HUFA-rich black soldier fly oil on the growth and health of juvenile mirror carp under the same supplemental levelsIn order to compare the effects of dietary black soldier fly oils with different nutrition properties(two black soldier fly oils prepared from algal residue and bran as dietary sources respectively)on growth performance,lipid metabolism,antioxidant capacity,inflammation and related gene expression of juvenile mirror carp.Three isonitrogenus and isolipidic diets,Control,W-B and A-B were formulated by supplementing with 25 g kg-1 different oils including soybean oil,black soldier fly oil fed on wheat bran(W-BSFO)and black soldier fly oil fed on algae residue of Schizochytrium(A-BSFO),respectively.Triplicate cages of juvenile mirror carp(15 fish per cage,initial mean body weight,10.04±0.08 g)were fed on one of the three diets above respectively.After 56 days,(1)the growth of fish fed A-B diet were significantly higher than fish in another two groups(P<0.05);(2)IFI and adipocyte size decreased in intra-peritoneal fat tissue of fish fed on diets containing black soldier fly oil compared to fish fed on Control diet(P<0.05).Relative gene expression of PPAR-?and CPT-1 significantly increased in intra-peritoneal fat tissue of fish fed on diets containing black soldier fly oil(P<0.05);(3)The intestinal villus height was significantly longer in fish fed on A-B diet compared to fish fed on Control and W-B diets(P<0.05);(4)The content of serum alanine transaminase(ALT)was significantly lower while the TP,GLO and LZM content were significantly higher in fish fed A-B diet compared to fish fed Control and W-B diets(P<0.05).(5)The activity and transcription of total SOD significantly increased in hepatopancreas of fish fed A-B diet than fish fed Control and W-B diets(P<0.05).The transcription of pro-inflammatory cytokine IL-1?and TNF-?was significantly lower in hepatopancreas and kidney tissues of fish fed on A-B diet(P<0.05).Overall,both W-BSFO and A-BSFO are potential lipid source in aquatic feeds,and they could improve lipid metabolism in intra-peritoneal fat of fish.Furthermore,A-BSFO has more positively influence on growth performance,intestinal health,liver antioxidant capacity and inflammatory response of juvenile mirror carp than W-BSFO.To sum up,(1):Extraction and pressing method can be used as the methods to prepare black soldier fly oil;(2)From the perspectives of growth,lipid metabolism and inflammatory response,black soldier fly is a better feed oil for insect aquatic products than silkworm pupa oil and yellow mealworm oil;(3)Dietary black soldier fly oil can effectively reduce lipid accumulation in juvenile mirror carp by promoting lipolysis.However,the regulation effect of black soldier fly oil on lipid metabolism in high lipid diet was not as obvious as that in low lipid diet;(4)Using algal residue rich in n-3 HUFA as the culture substrate,the corresponding fatty acid levels in black soldier fly oil could be increased,and the obtained black soldier fly oil could promote the growth,lipid metabolism of intra-peritoneal fat tissue,and enhance the antioxidant capacity and anti-inflammatory ability of hepatopancreas of juvenile carp. |
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