| The Pelteobagrus fulvidraco was a most important and famous fish specie in freshwater aquaculture which had a wide range of market prospect.In recent years,its artificial breeding technology had been gradually perfect,but the fry and microdiets were major factors restricting development of the fish.The researches about nutritional needs and microdiet of Siluriformes larvae focused on protein,lipid and fatty acid,etc.There was few research for fish larvae under recirculating aquaculture system(RAS)conditions.However,the study about lipid and protein nutritional needs on Pelteobagrus fulvidraco larvae under recirculation aquaculture system was blank.This experiment under RAS,aimed to investigate the effects of change and interaction of lipid and protein levels on survival,growth performance,physiological metabolism and antioxidation of Pelteobagrus fulvidraco larvae,and achieved the appropriate levels of nutrients,and provided valuable theory basises and pactical references for development of microdiets of fish larvae under RAS.This study with the theories and methods of subjects,such as symptomatologic nutrition,ecological nutrition,physiological and biochemical,fish biology,biostatistics,etc.,as guides,aimed to research the effects of lipid and protein nutrition on growth performance,physiological metabolism and antioxidation in P.fulvidraco larvae under RAS.A random 2×2 two-factors animal experiment which including two different protein levels(48%,52%)and two lipid levels(9%,13%)was used to formulate 4 trial diets(P52L13?P52L9?P48L13?P48L9).Each treatment had 3replicates and 3600 trial fishes per replicate.The trial fish was “All-Male No.1” P.fulvidraco larvae at 2 day after hatching that fed Artemia nauplii as initial feeding for1 day,and gradually transform to trial diets.The conversion period of feed was 2 days.The research was conducted for 21 days.Meanwhile,to explore the different effects of two kinds of compound feeds on the larvae survival and growth performance.The test feed was P52L13 diet,and the control feed was internationally excellent and imported feed.The results showed as follows:1.The results of growth showed that the change and interaction of dietary lipid and protein levels had significantly effects on the survival rate(SR),weight gain rate(WGR)and feed conversion rate(FCR)of P.fulvidraco larvae.High lipid level of diets significantly improved SR,and high protein level of diets significantly improved WGR and FCR of the larvae(P<0.01).P52L13 diet significantly increased SR of trial fish compared with P52L9,P48L13 and P48L9 diet,and increased by 32.67%(P<0.01),22.21% and 14.54%(P<0.05),respectively.The WGR of trial fish fed with P52L13 diet increased by 40.15% and 43.74% compared with P48L13 and P48L9 diet(P<0.05).P48L9 diet improved SR by 15.83%(P<0.05)compared with P52L9 diet,but WGR was the lowest.The new discovery of this study was that lower protein and lipid levels had negative effects on trial fish growth,but benefited survival ability when the protein to lipid ratio was appropriate(This trail was 4.00~5.33).2.The results of main growth hormones showed that appropriate nutrients levels and interaction were very important for them of P.fulvidraco larvae.High protein and lipid level of diets significantly improved IGF-1and T3 levels(P<0.05 or P<0.01).P52L13 diet significantly increased IGF-1 levels by 46.2%(P<0.05)compared with P48L9 diet.P48L9 diet had the lowest IGF-1?T3 and GH levels,and IGF-1 levels significantly lower than others by 25.76%~31.6 %(P<0.05).It was the reason that P48L9 diet had an negative effect on WGR.3.Digestion and absorption results showed that high protein level of diets was significantly improved Na+-K+-ATPase activity.The enzymes activity of digestive and absorption of trail fish fed with P52L13 diet were higher than others(P<0.05 or P>0.05),and AKP activity giving 16.71% and 14.57% higher than P52L9 and P48L13(P<0.05).It turned out that P52L13 diet benefited to improve digestion and absorption capacity of P.fulvidraco larvae.P48L9 diet had a tendency to improve the capacity,this was why P48L9 diet had an negative effect on trial fish growth,but benefited to survival ability.4.Metabolic enzymes of lipid and protein results showed as follows: High lipid level of diets significantly improved LPL and GOT activity(P<0.05 or P<0.01).Low protein level of diets significantly improved FAS activity.P52L13 and P48L9 diets increased LPL activity by 57.5%~80% and 35%~60%(P<0.01)than others,and improved GPT activity by 32.96% and 24.81%(P<0.05)compared with P48L13 diet.It indicated that LPL and GPT had important implications for survival and growth of the larvae.This was the mechanism of lipid and protein metabolism for diets with appropriate protein to lipid ratio to improve survival of P.fulvidraco larvae.5.Immunity and anti-oxidation capacities results were as follows: Both high protein level and high lipid level of diets were significantly increased SOD?CAT and LZM activities(P<0.05 or P<0.01).However,low protein and lipid level of diets had improved GSH activity.P52L13 and P48L9 diets increased SOD and CAT activity by 16.00%~80.00%(P<0.01 or 0.05)and 12.08%~62.96%(P<0.05)than P52L9 and P48L13 diets.P52L13 diet increased LZM activity by 29.21%~34.43%(P<0.05)than others,but decreased MDA levels by 11.11%(P<0.05)than P48L9 diet.The GSH activity of the larvae fed with P48L9 was improved by 6.75% ~41.92%(P<0.05)than others.The preliminary new discovery was that the mechanism of immunity and anti-oxidation for P48L9 and P52L13 improved growth performance,not only had commonality,but also existed pathways.The mechanism made P52L13 and P48L9 both improved survival of the larvae,and P52L13 increased weight gain of the larvae.6.The contrast experiments between P52L13 diet and the imported internationally excellent feed showed that growth performance indices of the two diets had no significant difference(P>0.05).The survival rate in P52L13 group was4.88% higher than control group,but the weight gain rate and average daily feed intake in control group were 11.02% and 11.66% higher than P52L13 group.Thosesuggested that P52L13 diet could meet the nutritional requirement of survival and growth of P.fulvidraco larvae.The effects of P52L13 diet on larvae growth performance was similar or superior to control diet,but its protein level and processing technology were necessary to be perfected.In addition,the daily survival of two groups both decreased first rapidly then slowly,because of the critical period of fish larvae development,and first feeding compound diets.It indicated that the two kind of diets inferior to live food in physical and biological properties of particles,such as suspension property,hardness,fresh,etc.They need further improved and perfected to become fish larvae first feeding diets.7.The preliminary new discovery of this study was that:(1)The low protein and lipid diet(P48L9)had no favorable on growth performance,but benefited survival ability of the larvae because of its protein to lipid ratio.The initial physiological mechanism was that P48L9 diet improved enzymes activities of digestion and absorption and partial anti-oxidation and immune,but had no advantages to the main growth hormone levels and related metabolic enzyme activity.Therefore,the protein to lipid ratio of diets played an important role in early development of fish life.(2)The mechanism of immunity and anti-oxidation for P48L9 and P52L13 improved growth performance,not only had commonality,but also existed pathways.The commonality was that the two diets simultaneously increased SOD?CAT activities to improve anti-oxidation ability of the larvae.The pathways were that P52L13 diet increased LZM activity and decreased MAD levels to improve immunity,and P48L9 diet increased GSH activity to improve anti-oxidation ability.The mechanism made P52L13 and P48L9 both improved survival of the larvae,and P52L13 increased weight gain of the larvae.In conclusion,the experimental study indicated that the change and interaction of lipid and protein have significantly affect on survival,growth and physiological metabolism of P.fulvidraco larvae.This study preliminary determined that P52L13 diet was the excellent combination that improved SR,growth performance,growth hormone,digestion and absorption ability,physiological metabolism and antioxidant ability of P.fulvidraco larvae under RAS.The P48L9 diet with appropriate protein tolipid ratio could enhance survival,digestion and absorption ability,physiological metabolism and antioxidant ability of P.fulvidraco larvae.The effects of P52L13 diet on larvae growth performance was similar or superior to control diet.Therefore,the appropriate and equilibrium protein and lipid levels of diets were key material basis that promoting and improving the development,survival and growth of P.fulvidraco larvae. |
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