| Due to the limited resource and increasing price of fishmeal,exploiting new protein sources to reduce fishmeal inclusion in aquafeed has attracted more and more attention.In this study,largemouth bass(Micropterus salmoides)was used as the experiment animal focusing on flesh quality.First,the growth and flesh qualiy of largemouth bass fed trash fish and fed formula feeds were compared,then the utilization potential of cottonseed protein concentrate replacing fishmeal was evaluated through growth performance,nutrient utilization,flesh quality,intestine health,serum biochemical indicators and metabonomics.Based on the above results,amino acids,taurine,hydroxyproline,chlorogenic acid,and Eucommia ulmoides leaf extract were supplemented in a low fishmeal diet containing high cottonseed protein concentrate to improve growth performance and flesh quality.This study provides theoretical basis for application of CPC in carnivorous fish feed and preparation of low fishmeal feed for largemouth bass.1.The comparison of largemouth bass(Micropterus salmoides)fed trash fish and formula feeds:growth,flesh quality,histology and metabolomicsTo compare the growth,flesh quality and metabolomics of largemouth bass(Micropterus salmoides)fed trash fish and formula feeds,trash fish(TF),self-made feed(SF)and commercial feed(CF)were fed to largemouth bass with an initial body weight of 75.0 g for 12 weeks.The crude protein levels of the three feeds were 172.2 g/kg,503.5 g/kg and 504.1 g/kg respectively(666.2 g/kg,547.3 g/kg and 535.1 g/kg dry matter).Compared to TF group,SF and CF groups presented significantly lower feed intake(FI),feed conversion ratio(FCR)and higher protein efficiency ratio(PER)based on dry matter basis(P<0.05),but no significant difference in weight gain(WG).was found among the three groups(P>0.05).The yellowness(b*)in dorsal muscle,flesh heat-insoluble collagen and free delicious amino acids contents in SF group were significantly higher(P<0.05),while drip loss(at 6th h,12th h and 24th h)were significantly lower(P<0.05)than those of TF group.Compared to TF group,SF and CF groups showed significantly higher flesh polyunsaturated fatty acids(PUFAs),n-3 PUFAs and n-6 PUFAs contents,flesh hardness,shear force and muscle fiber density(P<0.05),and lower flesh total free amino acids,essential amino acids,muscle fiber diameter,intestine villus height and muscular thickness(P<0.05).The serum total protein,triglyceride and cholesterol levels in SF group were significantly lower than those in TF and CF groups(P<0.05).In muscle metabolomics,177 differential metabolites were detected between SF and TF groups,which mainly enriched in pathways as biosynthesis of amino acid,protein digestion and absorption,histidine metabolism,glycine,serine and threonine metabolism,etc.Conclusively,feeding largemouth bass with formula feeds improved flesh fatty acid profile and flesh texture without negative effects on growth,but the flesh free amino acids contents were lower than the fish fed trash fish.2.Effects of replacing fishmeal with cottonseed protein concentrate in high fishmeal diet on growth performance,flesh quality and safety characteristics of largemouth bass(Micropterus salmoides)This study evaluated the effects of substituting fishmeal with cottonseed protein concentrate(CPC)in high fishmeal diet on growth,flesh quality and security of largemouth bass,Micropterus salmoides.A basal diet was formulated to contain 700 g/kg fishmeal,and then CPC was used to replace 0%(FM),15%(C15),30%(C30),45%(C45),70%(C70)and 100%(C100)of dietary fishmeal.The six diets were fed to largemouth bass with initial body weight of 95.3 g for 12 weeks.The results indicated that 45%of fishmeal could be successfully replaced by CPC without significant impacts on weight gain(WG)and feed conversion ratio(FCR)(P>0.05),while WG was decreased and FCR was increased when 70%fishmeal was replaced by CPC.The retention efficiencies of crude protein and essential amino acids were affected linearly or quadratically by dietary CPC levels(P<0.05).Compared to FM group,the flesh composition(crude lipid,amino acids contents)and texture(chewiness,cohesiveness and shear force)were decreased significantly in C70 group,while higher polyunsaturated fatty acids level was found in C15-C70 groups(P<0.05).In water-holding capacity,higher flesh drop loss at 12th h and lower centrifugal loss were observed in C15-C70 groups than those in FM group(P<0.05).All CPC groups showed significant lower serum cholesterol content than the FM group(P<0.05).The serum glucose,triglyceride and total protein contents in C70 group were significantly lower than those in FM group(P<0.05).In flesh safety characteristics,the contents of heavy metals(Cd,Pb,Hg and As)were in the 0.03-0.04 mg/kg,0.1-0.2 mg/kg,0.01-0.03 mg/kg and 0.2-0.7 mg/kg range,lower than the limitation of poisonous and harmful substances in aquatic products.The free gossypol contents in flesh of FM,C45 and C70 groups were within 0.25-0.30 mg/kg.Conclusively,up to 45%fishmeal could be successfully replaced by CPC without compromising the growth,flesh composition,texture,flavor characteristics and antioxidant capacity,while 70%fishmeal replacement by CPC produced negative effects on the growth performance and flesh quality of largemouth bass.3.Effects of replacing fishmeal with cottonseed protein concentrate in high fishmeal diet on largemouth bass(Micropterus salmoides)based on amino acids balanceBased on the results of Expt.2,taurine,methionine,lysine,threonine,isoleucine,leucine,valine and histidine were supplemented in C15,C30,C45,C70 and C100 diets(CA15,CA30,CA45,CA70 and CA100)to form another five diets with the similar levels to the control diet(FM).The six diets were fed to largemouth bass with an initial average body weight of 95.3 g for 12 weeks.The results showed that the weight gain(WG),feed conversion ratio(FCR),feed intake and protein retention ratio(PRE)were linearly and quadratically affected by dietary CPC levels(P<0.05).When 100%fishmeal was replaced by CPC(CA100),the WG was decreased by 52.3%,and FCR was increased by 0.34(P<0.05).Compared to FM group,flesh shear force of CA100 group was significantly decreased(P<0.05),while CA70 and CA100 groups showed lower flesh cohesiveness,chewiness and higher drip loss(at 12th h)(P<0.05).The contents of total free amino acids(TFAAs),delicious amino acids(DAAs)and essential amino acids(EAAs)in flesh were linearly and(or)quadratically affected by dietary CPC levels(P<0.05).Significant linear effect of dietary CPC levels were observed on the contents of flesh n-3 polyunsaturated fatty acids(n-3 PUFAs)and n-6 polyunsaturated fatty acids(n-6 PUFAs)(P<0.05).In conclusion,up to 45%fishmeal could be successfully replaced by CPC without compromising the growth,flesh texture and antioxidant capacity,while 70%fishmeal replacement by CPC increased FCR and flesh drip loss,and decreased flesh cohesiveness and chewiness.4.Effects of replacing fishmeal with cottonseed protein concentrate in practical diets on growth and flesh quality of largemouth bass(Micropterus salmoides)The study estimated the effect of substituting fishmeal with cottonseed protein concentrate(CPC)in practical diets on growth performance and flesh quality for large largemouth bass(Micropterus salmoides).In a basal diet with fishmeal inclusion of 400g/kg,five diets were formulated with CPC inclusion to replace 0%(FM40),15%(FM34),30%(FM28),45%(FM22)and 60%(FM16)of fishmeal,then fed to largemouth bass with initial body weight of 75.0 g for 12 weeks.The results showed that 15%and 30%of dietary fishmeal could be replaced by CPC without significant effect on the weight gain(WG)and feed conversion ratio(FCR)of largemouth bass(P>0.05),while 45%and 60%of dietary fishmeal was replaced by CPC,the WG was decreased by 17.2%and FCR was increased by 0.19(P<0.05).With the increase of replaced fishmeal levels by CPC,the flesh hardness and heat-insoluble collagen content showed a significantly negative linear trend(P<0.05),while flesh drip loss(at 12th h and 24th h),n-6 polyunsaturated fatty acid,total free amino acids and delicious amino acids contents showed a significantly positive linear trend(P<0.05).FM22 and FM16 groups showed lower flesh hardness and higher drip loss(24 h)than FM40 group(P<0.05).The substitution of fishmeal by CPC linearly and(or)quadratically affected serum glucose,triglyceride and cholesterol contents(P<0.05).In muscle and intestinal histology,muscle fiber density and intestine villus height in FM16 group were significantly increased,while flesh fiber diameter in FM16 group and intestine villus width in FM28,FM22 and FM16 groups were significantly decreased when compared to FM40 group.In muscle metabolomics,97 differential metabolites were detected between FM16 and FM40 groups,which mainly enriched in pathways as biosynthesis of amino acid,D-arginine and D-ornithine metabolism,histidine metabolism,alanine,aspartate and glutamate metabolism,etc.Conclusively,in a basal practical diet containing 400 g/kg fishmeal,CPC could replace 30%fishmeal(120 g/kg)without significant impacts on growth,flesh composition,texture,flavor characteristics and muscular tissue structure.However,45%fishmeal(180 g/kg)replacement by CPC decreased growth performance and flesh quality of largemouth bass.5.Effects of supplementating functional additives in low fishmeal diet on growth and flesh quality of largemouth bass(Micropterus salmoides)The study investigated the effect of functional additives supplementation in low fishmeal and high CPC diet on the growth and flesh quality of largemouth bass.A basal diet was formulated to contain 400 g/kg fishmeal(FM40),and then CPC was used to replace 60%fishmeal(FM16).Then,10 g/kg taurine(TAU),6 g/kg hydroxyproline(HYP),0.4 g/kg chlorogenic acid(CGA)and Eucommia ulmoides leaf extract(ELE)were individually supplemented into FM16 diet.The six diets were fed to largemouth bass with initial body weight of 75.0 g for 12 weeks.The results showed that the weight gain(WG)was significantly decreased,and feed conversion ratio(FCR)was significantly increased when 60%fishmeal was replaced by CPC(P<0.05).Compared to FM16 group,the supplementation of hydroxyproline in low fishmeal diet significantly increased WG(+11.4%)and decreased FCR(-0.11)(P>0.05)with the similar growth to the FM40 group(P>0.05).The supplementation of taurine,chlorogenic acid and Eucommia ulmoides leaf extract in FM16 group had no significant effect on the growth of largemouth bass(P>0.05).Compared to FM16 group,dietary supplementation of hydroxyproline showed higher flesh total collagen and heat-insoluble collagen contents,and lower the drip loss(at 12th h and 24th h)(P<0.05).The content of flesh heat-insoluble collagen in ELE group,the flesh total amino acids content in CGA group were significantly higher than those in FM16 group(P<0.05).The supplementation of taurine,hydroxyproline,chlorogenic acid and Eucommia ulmoides leaf extract significantly decreased the average muscle fiber density and intestinal muscle thickness,and increased the average muscle fiber diameter and intestinal villus width(P<0.05).In summary,the supplementation of 10 g/kg of taurine,6.0 g/kg of hydroxyproline,0.4 g/kg of chlorogenic acid or 1.0 g/kg of Eucommia ulmoides leaf extract in low fishmeal diet containing 160 g/kg fishmeal did not affect the growth performance of largemouth bass.Dietary hydroxyproline,chlorogenic acid and Eucommia ulmoides leaf extract improve the flesh quality and intestinal health by improving flesh collagen content,texture,flesh fiber structure and intestinal morphology. |
