Study On The Application Of Defatted Black Soldier Fly Larvae Meal In The Formulated Diets For Juvenile Large Yellow Croker (Larimichthys Crocea)

This study was conducted,firstly,to determine the nutritional composition and apparent digestibility of defatted black soldier fly larvae meal?DBSFLM?for juvenile large yellow croakes Larimichthys crocea.Then,in order to assess the effects of replacement of dietary fish meal?FM?with DBSFLM on growth performance,feed conversion,intestinal digestive enzyme activities,muscle nutritional composition,serum biochemical indexes,liver antioxidant enzyme activities and expression of some protein metabolism related genes in large yellow crokers.Six isonitrogenous?45%crude protein?and isolipidic?10%crude lipid?diets were formulated by replacing 0%,20%,40%,60%,80%and 100%of FM protein with DBSFLM?designated as G0,G20,G40,G60,G80,and G100,respectively?.A total of 2160 juvenile large yellow croakes with an initial body weight of?50.08±3.31?g were randomly divided into six groups with three replicates,and 120 individuals for each replicate.Fish were reared in an indoor cement tank?2m×1m×1m?and were hand-fed each diet to apparent satiation twice daily for 7 weeks.The experimental results and conclusions are summarized as follow:1)Study on nutritional composition and apparent digestibility of DBSFLM for juvenile large yellow croakes.The DBSFLM used in this study contained 37.78%crude protein,11.37%crude lipid and 12.47%crude ash of dry matter,respectively.DBSFLM have high contents of valine,leucine,isoleucine and lysine as well as low contents of methionine in essential amino acids.The contents of glutamic acid,tyrosine,alanine and aspartic acid were high in non-essential amino acids.The apparent digestibility of the dry matter,crude protein and crude lipid of DBSFLM were60.27%,81.25%and 82.13%,respectively.2)Effects of replacement of dietary FM by DBSFLM on growth performance,feed utilization,intestinal digestive enzyme activities of juvenile large yellow croaks.The weight gain rate?WGR?,specific growth rate?SGR?,feed efficiency rate?FER?and protein efficiency?PER?of juvenile large yellow croakers were highest in G40 group which significantly higher than those in the control group?G0 group??P<0.05?and lowest in G100 groups which significantly lower than those in the G0 group?P<0.05?.These parameters showed a trend from increase to decline with theincreaseofdietaryDBSFLMlevel.Thehepatosomatic index?HIS?and viscerosomatic index?VSI?of juvenile large yellow croakers increase with the increase of dietary DBSFLM level.The activity of intestinal amylase were significantly increase when fish fed diets replaced up to or over 60%FM protein by DBSFLM.The activity of intestinal lipase and trypsin showed first increased and then decreased with the increase of dietary DBSFLM level.The activity of intestinal trypsin reached maximum in the G20 group and the activity of intestinal lipase was highest in G40 group and lowest in G100 group,respectively.3)Effects of replacement of dietary FM by DBSFLM on muscle nutritional composition of juvenile large yellow croakers.The body crude protein content of juvenile large yellow croakers showed a downward trend with increase of dietary DBSFLM level,and decreased remarkably when dietary FM protein was replaced by DBSFLM up to or over 40%?P<0.05?.The body crude lipid and crude ash content showed a decrease trend and increased significantly when dietary FM protein was replaced by DBSFLM up to or over 60%?P<0.05?.The total amount of essential amino acids?TEAA?,total non-essential amino acids?TNEAA?and total amino acid?TAA?in the muscles of large yellow croakers were the highest in the G20 group.The TEEA,methionine and histidine content in fish muscle showed decreased significantly with increase of dietary DBSFLM level.The total saturated fatty acids??SFA?content in muscle of the large yellow croakers was significantly increased,while the total monounsaturated fatty acids??MUFA?,EPA and DHA content decreased significantly when the FM protein substitution level was up to or over 20%?p<0.05?.4)Effects of replacement of dietary FM by DBSFLM on serum biochemical indexes and liver antioxidant enzyme activities of juvenile large yellow crokers.The activities of serum alanine aminotransferase?ALT?,and aspartate aminotransferase?AST?as well as serum GLU level of fish increased with increasing dietary DBSFLM level.Serum ALT and AST activities have no significant difference?P>0.05?between G20 and G40 groups,but significantly lower than that of higher level FM protein substitution groups?P<0.05?.Serum triglyceride?TG?level of fish was highest in G40 groups and showed a decrease trend with increasing dietary DBSFLM level.The serum HDL levels of fish showed decreased significantly when dietary FM protein was replaced by DBSFLM up to or over 40%?P<0.05?.Serum LDL and CHOL levels of fish also showed decreased significantly when dietary FM protein was replaced by DBSFLM up to or over60%?P<0.05?.The level of serum Na⁺and K⁺showed up down fluctuation pattern.Fish fed high inclusion level of DBSFLM diet showed significantly lower level of serum Ca²⁺than those fed inclusion low level of DBSFLM diet?P<0.05?.Total antioxidant capacity?T-AOC?and superoxide dismutase?SOD?activity of fish liver were highest in G20 group and liver malondialdehyde?MDA?level was the lowest in the G40 group,while the activity of catalase?CAT?decreased with the increase of FM protein substitution level.The activity of CAT showed significantly decreased?P<0.05?when dietary FM protein was replaced by DBSFLM up to or over 40%.5)Effects of replacement of dietary FM by DBSFLM on expression of protein metabolism related genes in juvenile large yellow croakers.The PepT1 gene showed trace level expression in liver and muscle of juvenile large yellow croakers in G0 and G40 group and the expression level of PepT1 gene in liver,intestine and muscle was significantly higher than that in G0 and G40groups?P<0.05?,but there were no significant difference between G0 and G40 groups?P>0.05?.The expression level of Trypsin gene in liver and intestine of fish in G40 group was significantly higher than that in G0 and G100 groups?P<0.05?,while only the trace level expression of Trypsin gene in fish muscle were found among all groups.The lower expression level of CCK gene were found in muscle and liver of fish in G0 and G40 group while expression level of CCK in liver,intestine and muscle of fish in G100 group was significantly higher than that in G0 and G40 groups?P<0.05?.Also there was no significant difference between G0 and G40 group?P>0.05?.In G100group,the expression level of TOR gene in fish liver,intestine and muscle were significantly higher than those in G0 and G40 group?P<0.05?and also there was no significant difference of gene expression levels in liver,intestine and muscle of fish between G0 and G40 groups?P>0.05?.In conclusion,results of the present study show that the replacement of dietary FM protein with DBSFLM up to 40%had no marked effects on growth performance and health of juvenile large yellow croakes.