Effects Of Replacement Of Dietary Fishmeal By Maggot Meal On Growth Performance,Digestion And Intestinal Healthy In Japanese Seabass(Lateolabrax Japonicus)

This study evaluated the effects of substituting dietary fish meal（FM）with housefly（Musca domestica）maggot meal（HFMM）on growth performance,diet digestibility,and gut and liver health in Japanese seabass（Lateolabrax japonicus）.Five isonitrogenous and isolipidic diets were formulated by replacing 0,20,40,60 or 80%of FM with HFMM.Quadruplicate groups of30 fish（initial body weight 5.80±0.07g）were fed the test diets to apparent satiation twice daily（08:00 and 16:30）for 70 days.During the feeding trial,water temperature,salinity and dissolved oxygen values were 29.5±1.5°C,29±1‰,and 6.5±1 mg L^-1,respectively.Results of the study were as follows:1.Effects on growth,body composition,digestive enzyme activities and apparent digestibility coefficientsThe results showed that substituting 20%of FM with HFMM does not significantly affect growth performance（P>0.05）,while further increment of replacement level resulted in significantly reduced weight gain,feed efficiency,protein efficiency ratio and survival rate（P<0.05）.Whole-body protein content significantly decreased by FM replacement,whereas moisture,lipid and ash contents were not significantly affected.FM replacement led to significant reduction of protease activity.Apparent digestibility coefficients（ADCs）of protein,lipid and dry matter decreased with increasing FM replacement level.These results showed that:increasing HFMM inclusion level in diets for Japanese seabass leads to decreased intestinal protease activity and ADCs,resulting in subsequent reduction of growth performance and whole0body body protein content.2.Effects on posterior intestine and liver morphologyHistological observations showed a normal gut mucosa and posterior intestine structure in the FM group.Number of goblet cells in gut mucosa increased at over 40%replacement level.Also,increasing FM replacement level resulted in decreased intestinal mucosal fold and villus height and increased lamina propria thickness,and intestinal epithelial cells vacuolization.No significant changes were observed in fish liver structure;all groups showed normal hepatocytes morphology,structural integrity,uniform arrangement and the nucleus was regularly round in the cell center,no offset and vacuolization,and clear hepatic cord.Also,no significant alteration in serum AKP,GOT,GPT activities and T-AOC were found among groups（P>0.05）.These results indicated that:replacement of FM with HFMM damages posterior intestine structure,but has no adverse impacts on liver health.3.Effects on intestinal inflammatory genes expression and gut microbiotaIncrement of FM replacement level resulted in significant enhancement of gut inflammatory genes expression such as TNF-α,IL-1β,while an opposite trend was observed for expression of IL-4and IL-10 genes.Microbial genome sequencing showed no significant changes in diversity of intestine microbiota,however,the flora structure was different.