Effect Of Yellow Mealworm(Tenebrio Molitor) Protein On Extruded Feed Quality And Intestinal Immune Function Of Largemouth Bass(Micropterus Salmoides)

As a new non-grain protein resource,insect protein is widely applied in feed and food industries.This study aimed to describe the effect of the physicochemical properties of defatted yellow meal protein(Tenebrio Molitor,YM)on the quality of extruded feed.We also used largemouth bass(Micropterus salmoides)as an enteritis model animal to explore the effect of YM on the growth performance and intestinal immune function of largemouth bass.Experiment 1:Effect of YM on feed quality and apparent digestibility coefficients of nutrients of largemouth bass.This study investigated the effect of the YM as an alternative to fishmeal on the quality of extruded feed and the apparent digestibility coefficients(ADC)of nutrients in largemouth bass.In this experiment,three levels of yellow meal protein substitution for fishmeal were established:0%(YM0),50%(YM50),and 100%(YM100).The results of the extrusion experiment indicated that the YM50group had the optimum feed quality and pellets microstructure.However,the YM100 group presented a higher bulk density and lower pellet porosity.In addition,the water absorption index and pasting properties of YM were revealed to be critical factors affecting the pellets quality based on the results of correlation analysis.The growth trial of largemouth bass indicated that the ADC of dry matter(ADC_d)and ADC of energy(ADC_e)in the YM50 group were significantly higher than those of other groups(P<0.05).According to the correlation analysis,the hydration time,hardness,expansion rate,and microstructure parameters of feed were significantly correlated with the ADC of nutrients(P<0.05).The results of this study showed that when YM substituted 50%of fishmeal in the feed formulation,it did not compromise the feed quality and ADC of nutrients in largemouth bass,but complete substitution of fishmeal will have a negative impact on feed quality and ADC of nutrients in largemouth bass.Experiment 2:Effect of YM on growth performance and intestinal health of largemouth bass.Based on the design of experiment 1,the amino acid composition of yellow meal protein and its effect on the growth performance and intestinal health of largemouth bass were further investigated.The experimental results found that the essential amino acid composition of YM had lower content of methionine,lysine,threonine,and histidine compared with fish meal.Therefore,if yellow meal protein is considered an alternative to higher levels of fish meal,the relevant amino acid content should be supplemented in the feed.When the level of yellow meal protein replacement for fishmeal was 50%,it did not comprise the growth performance and amino acid digestibility of largemouth bass,but YM complete substitution fish meal had adverse effects on the growth and amino acid digestibility of largemouth bass.The results of intestinal pathological analysis between all groups did not reveal any significant lesions.However,the expression levels of pro-inflammatory factors(TNFαand IL-1β)were significantly reduced in the YM50 group(P<0.05).In addition,the relative abundance of the harmful pathogen Chlamydiaceae was significantly increased in the YM100 group(P<0.05).The results of this study indicated that yellow meal protein is a well-balanced protein source of amino acids.When replacing 50%of fishmeal with YM,it did not compromise the growth and amino acid digestion of largemouth bass and it can reduce the expression of pro-inflammatory cytokines.However,its total replacement of fishmeal can lead to reduced growth of largemouth bass and disturbance of intestinal microbes.Experiment 3:YM regulates intestinal immunity function in largemouth bass.To further elaborate the immune mechanisms with fed YM to largemouth bass.Based on the growth trials,the levels of YM substituted for fishmeal were modified and the YM100 group with negative effects was removed.A 5-week Edwardsiella tarda(E.tarda)challenge trial was conducted.The experiment was designed with four levels of YM replacement fish meal,0%(EYM0),25%(EYM25),50%(EYM50),and 75%(EYM75),respectively.The experimental results indicated that the survival rate of largemouth bass was significantly increased in the EYM50 and EYM75 groups(P<0.05).Severe intestinal damage was observed in the EYM0 and EYM25 groups,mainly manifested by intestinal congestion,destruction of intestinal fold and goblet cells,dysregulation of tight junction proteins,intestinal cell apoptosis,and immunosuppression.However,the above-mentioned adverse phenomena were alleviated in the EYM50 and EYM75 groups.In immune mechanism studies,the EYM50 and EYM75 groups may regulate the transcription of the anti-apoptotic gene survivin by activating the TLR/My D88/IKK/NFκB signaling pathway in the intestine after E.tarda challenge,which in turn enhances intestinal immunity and cell anti-apoptotic function.The results of this study elucidate the protective mechanism of YM to improve intestinal health through NFκB/survivin signaling pathway.In conclusion,YM can replace up to 50%of fishmeal without negatively affecting the feed quality,growth performance,nutrients and amino acid digestibility of largemouth bass.Meanwhile,it can improve the intestinal immune and anti-apoptosis function of largemouth bass,and thus alleviate enteritis caused by pathogenic bacteria.