Study On The Effects Of Dietary Creatine Supplementation On The Growth Performance And Flesh Quality Of Pacific White Shrimp(Litopenaeus Vannamei) And Grass Carp(Ctenopharyngodon Idella)

The quality of aquatic products has become a common concern of consumers in recent years.For aquatic animals,the main material basis of flesh quality is the selective retention of nutrients from the diets.Therefore,it is the development trend of modern fishery to improve the quality of aquatic products through nutritional approaches.Creatine,one of the nitrogenous organic acids,had been found to improve muscle quality through increasing protein synthesis,regulating energy metabolism of muscle and affecting fiber characteristics and types on terrestrial animals.However,the effects and related mechanism of dietary creatine supplementation on the flesh quality of aquatic animals are not entirely known.Therefore,this project studied the effects of dietary creatine level on the growth performance and flesh quality of Pacific white shrimp(Litopenaeus vannamei)and grass carp(Ctenopharyngodon idella),which aimed to analyze the mechanism of dietary creatine on flesh quality improvement and provide new insights for the cultivation of high-quality aquatic products.Experiment 1: Effects of dietary creatine on the growth performance and flesh quality of Pacific white shrimp reared in freshwater.To study dietary creatine level on the growth performance and flesh quality of L.vannamei reared in freshwater,diets with six levels of creatine monohydrate(0%,0.15%,0.30%,0.60%,1.20% and 2.40%)were formulated(dietary creatine level measured in six diets was 0.12%,0.26%,0.51%,0.83%,1.41% and 2.45%,respectively)and hand-fed to juvenile L.vannamei(initial mean weight: 1.50 ± 0.02 g)for 46 days.Results showed that(1)creatine supplementation did not affect the growth performance and the content of guanidinoacetic acid in muscle and hepatopancreas(P > 0.05)whereas significantly increased creatine content in muscle and creatinine content both in muscle and in hepatopancreas,which were the highest when dietary creatine was 2.45%.(2)Muscular hardness and chewiness of L.vannamei were significantly higher than those of the control group when dietary creatine level was 0.83%(P < 0.05),the springiness,cohesiveness and resilience of muscle were not affected by creatine(P >0.05).(3)Dietary creatine with 0.83% significantly increased shrimp fiber density and myofibril sarcomere length,and decreased fiber diameter(P < 0.05).Additionally,dietary creatine significantly downregulated the m RNA level of fast s My HC1,s My HC2,s My HC6 a and upregulated slow s My HC5 and s My HC15 m RNA level(P < 0.05).(4)Shrimps fed diets containing 0.83% creatine had a significantly higher content of crude protein,alkaline-soluble and alkaline-insoluble collagen in the muscle(P < 0.05),while crude lipid,ash and moisture contents of muscle were not affected by dietary creatine(P > 0.05).(5)Creatine supplementation significantly affected the content of Asp,Ser,Glu,Gly,Arg,Phe and Lys in the muscle of L.vannamei,and the total content of essential amino acids and amino acids reached the highest when dietary creatine level was 1.41%.(6)Creatine increased the content of free flavor amino acids(Asp,Glu,Gly and Ala)in the muscle of L.vannamei and the total content of them was significantly higher than that of the control group when dietary creatine level was more than 0.51%(P < 0.05).In conclusion,creatine supplementation increased muscular creatine pool,improved flesh hardness,nutrition and flavor of L.vannamei through improving fiber characteristics,transforming fiber types,increasing the content of muscular collagen,protein,total essential amino acids and free flavor amino acids.The optimal dietary creatine concentration of L.vannamei was 0.83%.Experiment 2: Effects of dietary creatine on the growth performance and flesh quality of grass carpTo investigate the effects of dietary creatine on the growth performance and flesh quality of grass carp,four diets were formulated to contain graded creatine levels(0%,0.30%,0.60% and 1.20%),and creatine content measured in the four diets was 0.18%,0.59%,0.85% and 1.54%,respectively.Fish(initial mean weight: 88.47 ± 1.44 g)were artificially fed with the four diets for 8 weeks.At the end of the feeding trial,the results showed that(1)the growth performance of fish was not affected by creatine(P > 0.05).Creatine supplementation increased creatine content in fish muscle and liver,which were higher than that of the control group when dietary creatine was 1.54%(P < 0.05).(2)The highest muscle hardness and chewiness were observed in fish fed with 0.85%creatine compared to the control group(P < 0.05).(3)Dietary creatine with 0.85%significantly increased fiber density,sarcomere length and I-band width,and shortened fiber diameter(P < 0.05).Creatine supplementation significantly upregulated the m RNA expression of slow f My HCS30,f My HCS10 and myogenic regulatory factors(Myo D,Myo G and MRF4),and downregulated fast f My HCS and f My HCc m RNA expression(P < 0.05).(4)Grass carp fed diets with 0.85% creatine had a higher content of muscular protein than that of the control group(P < 0.05),while muscular crude lipid,ash,moisture and whole-body proximate composition were not different among the groups(P > 0.05).Creatine-fed fish had a higher content of alkaline-insoluble collagen and total collagen(P < 0.05).(5)Dietary creatine significantly affected the content of Asp,Glu,Gly,Met,Leu,Phe,Lys and Pro in the muscle of grass carp,and the total content of essential amino acids was higher when dietary creatine was 0.85%(P < 0.05).(6)Muscle in grass carp fed with 0.85% and 1.54% creatine had a significantly higher content of total flavor amino acids(Asp,Glu,Gly and Ala)than that of the control group(P < 0.05).In conclusion,dietary creatine improved fish flesh firmness through regulating myogenic regulatory factors,improving fiber density and diameter,transforming fiber from fast fiber type to slow fiber type and increasing muscular collagen content.Furthermore,creatine improved flesh nutrition and flavor through increasing the total content of essential amino acids and free flavor amino acids in fish muscle.The appropriate creatine content in the diet of grass carp was 0.85%.