Replacing Dietary Fish Meal With Defatted Black Soldier Fly （Hermetia Illucens） Larvae Meal Affected Growth,Biochemical Indexes,Intestinal Tissue Structure And Muscle Quality Of Chinese Tongue Sole （Cynoglossus Semilaevis）

For solving the global shortage of fish meal（FM）supplies from fisheries,black soldier fly（Hermetia illucens）has become a new protein alternative in aquatic feeds.The present study investigated the effects of dietary inclusion of defatted H.illucens larvae meal（DBLM）on growth,serum biochemical parameters,digestive function and muscle quality of half-smooth tongue sole（Cynoglossus semilaevis）.The feeding experiment consisted of five isonitrogenous（50%crude protein）and isolipidic（10%crude lipid）experimental diets:a control diet based on FM protein（H0）,four DBLM diets,substituting 25%(H₂₅),50%(H₅₀),75%(H₇₅)and 100%（H100）of FM.C.semilaevis（initial body weight 563.48±22.81 g）were randomly allocated over five treatments in quadruplicate.After 65 days feeding,the experimental results and conclusions were summarized as follow:（1）Effect of replacement of dietary FM by DBLM on growth performance,muscle nutritional composition of C.semilaevis.After 65 days of feeding,there was no significant difference in survival rate（SR）and condition factor（CF）among the five groups（P>0.05）,but SR was still high（90-100%）.With the increase of dietary DBLM level,weight gain rate（WGR）,instantaneous growth rate（IGR）and specific growth rate（SGR）all increased firstly,then decreased and finally increased,and the highest were in H₂₅group and the lowest were in H₇₅group.The feed conversion ratio（FCR）in H₀and H₂₅groups was significantly lower than that in H₅₀,H₇₅and H₁₀₀groups.At the same time,the FCR in H₇₅group was the highest.Protein efficiency（FER）increased firstly and then decreased with the increase of DBLM level,which was highest in H25 group and lowest in H75 and H100 group.Compared with the control group,feed intake was not significant effect in H₂₅and H₅₀groups（P<0.05）,but increased significantly in H75 and H100 groups.（2）Effects of replacement of dietary FM by DBLM on serum biochemical parameters,digestive function and liver biochemical parameters of C.semilaevis.The concentrations of serum ALT,TG,T-CHO,ALB,GLO and their ratio（i.e.A/G）in H₂₅group were also significantly higher than those in the other DBLM diets-feeding groups.The content of TG and T-CHO in H₅₀group were lowest.The content of malondialdehyde（MDA）decreased firstly and then increased with the increased level of DBLM in diets,and the content of MDA was the lowest in H₅₀group.The intestinal digestive enzyme activities firstly increased,then decreased with the increased level of DBLM in diets.The intestinal digestive enzyme activity in H₇₅group was the highest but significantly lower than that in H₀group.Meanwhile,there were significant improvements in the thickness of intestinal longitudinal muscle（LM）,circular muscle（CM）,columnar epithelium（CE）and lamina propria（LP）in H₂₅C.semilaevis compared to the control group（P<0.05）.The fish from the other DBLM diets groups presented significant reductions in thicknesses of LM,CM,CE and LP,as well as the length of microvill（ML）by a dose-dependent manner（P<0.05）.However,the substitution of FM increased up to 50%would result in intestinal structural damage.There was no significant difference in liver ALT activity among all groups（P>0.05）.Liver AST activity in H₂₅group was significantly higher than that in control group and H₁₀₀group（P<0.05）.The activity of GDH in liver in H₅₀,H₇₅and H₁₀₀groups was significantly higher than that in control group.With the increase of dietray defatted black horsefly larvae meal,the activity of GS in liver was decreased firstly,then increased and then decreased.（3）Effects of replacement of dietary FM by DBLM on muscle antioxidant and water holding capacity,muscular structures of C.semilaevis.There was no significant difference in CF among different treatments.Except for the DM,moisture,ash,CF and CP contents were significantly higher in H₂₅C.semilaevis muscles.The muscle CF and CP in H₁₀₀were significantly lowest.The DM was highest in H₅₀group which showed a trend from increase to decline and increase with the increase of dietary DBLM level.The muscle antioxidant and water holding capacity,muscular structures of C.semilaevis were all significantly affected after substituting 25%FM with DBLM（P<0.05）.The SOD activity in H0 group was greatly lower than that in the H₂₅group.The CAT activity in C.semilaevis muscles prominently reduced along with the raise in DBLM content in feeding diets（P<0.05）,and the activity in H₁₀₀group was lowest.The cooking loss rate,drip loss rate and freezing exudation rate in H₂₅group were the lowest or lower.The muscle fiber density increased firstly and then decreased with the increased level of DBLM in diets,and the maximum was found in H₂₅group.The minimum muscle fiber diameter in H₂₅group.Compared with H0group,muscle fiber clearance was significantly shortened in H₂₅,H₅₀and H₇₅groups,and the maximum clearance appeared in H₁₀₀group.The percentage of muscle fiber area in H₇₅group was significantly higher than that in other groups,and H₁₀₀group was the lowest.In summary,the optimum proportion of DBLM with FM for feeding C.semilaevis may around 25%.