Application Of Several Additives In Low Fish Meal Diet Of Rainbow Trout(Oncorhynchus Mykiss)

Due to the shortage of fishmeal resources and rising prices,reducing the dependence of carnivorous fish on fishmeal has always been a major research point in aquatic nutrition and feed.However,the unbalanced nutrients composition and low utilization of non-fishmeal proteins seriously restrict their application in feed.This paper investigated the effects of supplementing of enzyme,organic acid,essential oil,prebiotic,and butyric acid derivatives in low fishmeal diets on growth performance,immune function and intestinal health of rainbow trout.The research results can provide a theoretical basis for the development of low-fishmeal feed and promote the sustainable development of aquaculture.1 Supplementation of a multi-enzyme complex,an organic acid-essential oil complex,and prebiotic alone or in-combination affects growth,nutrient utilization and immune function of rainbow trout(Oncorhynchus mykiss)The present study aimed to investigate the dietary effects of a multi-enzyme complex,an organic acids-essential oil complexand prebiotic on growth,immune function and intestinal health of rainbow trout.A positive control diet(PC)and a negative control diet(NC)were formulated to contain 200 g/kg and 100 g/kg of fishmeal,respectively.Seven other diets were formulated by supplementing a multi-enzyme complex(MC,0.125 g/kg),organic acid-essential oil complex(OEC,0.5 g/kg)and prebiotic(P,2 g/kg)alone or in combination to the NC diet(MC,OEC,P,MC+OEC,MC+P,OEC+P,MC+OEC+P).All diets were formulated to be isoproteic(434.3 g/kg-439.1 g/kg)and isolipidic(119.2 g/kg-125.9 g/kg)and fed to rainbow trout of 7.66±0.05 g for 56 days.The weight gain,apparent digestibility coefficient of dry matter,protein efficiency ratio and protein retention efficiency were significantly increased,and feed conversion ratio was significantly decreased by the three additives alone or in combination(P<0.05)compared to the NC.No significant differences in growth performance and feed utilization were observed among the treatment groups.Compared to the NC group,serum alanine transaminase,aspartate transferase activities and malondialdehyde content reduced significantly,while serum superoxide dismutase increased in all except for the MC group,and alkaline phosphataseand lysozyme activity increased in all except for the MC and MC+P groups(P<0.05).The foregut protease activity of the MC+P and OEC+P groups and the amylase activity of the OEC and MC+OEC groups were significantly higher than those of the NC group(P<0.05).The villus height of P,MC+OEC and OEC+P groups,the villus width of MC group and the muscle thickness of MC,MC+OEC and MC+OEC+P groups were also significantly higher than those of the NC group(P<0.05).Compared to the PC group,the richness and diversity of intestinal microorganisms in the NC group and all the supplemented groups were significantly reduced(P<0.05),but no differences among them(P>0.05).In conclusion,the individual or combined supplementation of multi-enzyme complex,organic acids-essential oil complex and prebiotic in a low fish meal diet(100 g/kg)improved the growth performance,nutrient utilization,immune function of rainbow trout,but no synergistic effects were observed in the combination of the three supplements.2 Effects of citric acid and essential oil supplementation in low fish meal diets on growth performance,immune function and intestinal health of rainbow trout(Oncorhynchus mykiss)This study aimed to investigate the effects of citric acid(CA)and essential oil(EO)supplementation in a low fishmeal diet on growth performance,immune function and intestine health of rainbow trout.First,a positive control(PC)with fish meal inclusion of 200 g/kg and a negative control(NC)with fish meal inclusion of100 g/kg was designed.Then,1% CA,0.04% EO,1% CA+0.04% EO and 0.5% CA+0.02%EO were added in the NC diet to form four isonitrogenous and isolipidic diets.The six diets were fed to juvenile rainbow trout with initial body weight of35.00±0.06 g for 56 days.The results showed that weight gain(WG),protein efficiency ratio(PER),protein retention(PR)and digestive enzyme activity in the NC group were significantly lower,and feed coefficient ratio(FCR)was significantly higher than those in the PC group(P<0.05).Compared with the NC group,the supplementation of CA and EO alone or in combination significantly increased WG,PER,PR and reduced FCR of rainbow trout(P<0.05),reaching the similar levels to the PC group(P>0.05).However,the combined supplementation of CA and EO showed no significant difference in growth performance and feed utilization with the individually supplemented groups(P>0.05).Compared to the NC group,the supplementation of CA and(or)EO significantly decreased serum activity of alanine aminotransferase,aspartate aminotransferase and malondialdehyde content,while increased the alkaline phosphatase and protease activities(P<0.05).In addition,the lipase activity of 0.04%EO,1%CA and 1%CA+0.04%EO groups,the lysozyme activity of 0.04%EO and 0.5%CA+0.02%EO groups,and the foregut villus height,superoxide dismutase and amylase activities of 1%CA+0.04%EO group were significantly higher than those of the NC group(P<0.05).In the gut microbes,there was no significant difference in the microbiota composition among all the groups(P>0.05),and Firmicutes and Mycoplasma were the dominant phylum and genus in all the groups.The Simpson index of NC and CA,EO supplemented groups was significantly higher than that of the PC group(P<0.05).In conclusion,the supplementation of citric acid and essential oil in low fish meal(100 g/kg)diets alone and in combination,significantly improved the growth performance,feed utilization and immune function of rainbow trout,but the combination of citric acid and essential oil did not produce synergistic effects.3 Effects of dietary tributyrin and sodium butyrate supplementation in low fish meal diets on growth performance,immune function and intestinal histology of rainbow trout(Oncorhynchus mykiss)The purpose of this study was to investigate the effects of tributyrin and sodium butyrate supplementation in low fishmeal diets on the growth performance,immune function and intestinal histology of rainbow trout.A positive control diet(PC)and a negative control diet(NC)were designed to contain 200 g/kg and 100 g/kg fish meal,respectively.Then,1.5 g/kg tributyrin(TB)and 2 g/kg sodium butyrate(SB)were supplemented to NC diet,respectively.The 4 isonitrogenous and isolipidic diets were fed to rainbow trout with initial body weight of 35.00±0.06 g for 56 days.The NC group showed significantly lower weight gain(WG),protein efficiency rate(PER),protein retention(PR),and higher feed coefficient ratio(FCR)than the PC group(P<0.05).The supplementation of tributyrin and sodium butyrate did not significantly affects the WG,PER,PR and FCR(P>0.05).Compared to the NC group,the TB and SB groups significantly decreased the alanine aminotransferase,aspartate aminotransferase activities and malondialdehyde content,and increased the alkaline phosphatase activity(P<0.05).In addition,lysozyme activity and intestinal villus height of TB group were significantly higher than those in the PC group(P<0.05).In conclusion,the supplementation of 1.5 g/kg TB and 2 g/kg SB in low fish meal(100g/kg)diet had no significant effect on growth performance and feed utilization,but improved the immune function of rainbow trout.