Effect of partial black soldier fly (Hermetia illucens L.) larvae meal replacement of fish meal in practical diets on the growth, digestive enzyme and related gene expression for rice field eel (Monopterus albus)

A ten-week feeding trial on Monopterus albus (initial weight 24.02 +/- 0.02 g) was conducted to evaluate effects of four isonitrogenous and isoenergetic diets in which different proportions of fish meal (0, 2.5 %, 5% and 7.5 %) were substituted with Hermetia illucens (HI) larvae meal, corresponding to dietary inclusion levels of 0 (FM), 5.26 (HI5.26), 10.52 % Mho 52) and 15.78 % (HI15.78). Compared with FM, weight gain rate and condition factor of M. albus and gumminess and adhesiveness of its muscle tissue were significantly increased in HI5.26 and Hi(10.52) groups (P < 0.05); whereas feed conversion ratio was markedly decreased in HI, 26 (P < 0.05), and expression of hepatic FASD2 and ME2 was significantly upregulated in HI5.26 (P < 0.05). Compared with FM, cohesiveness of muscle was significantly decreased in HI groups, but hardness of muscle and expression of hepatic FAS were remarkably upregulated in HI groups (P < 0.05); ACC and ME1 mRNA levels were significantly upregulated in HI10.52 (P < 0.05); CPT2 mRNA levels were significantly upregulated in HI, 26 and HI15.78 (P < 0.05); PPARy, G6PD and HSL mRNA levels were significantly upregulated in Hi(10.52) and HI15.78 (P < 0.05). Springiness and chewiness of muscle, activity of intestinal lipasewere, serum indexes (glutamic oxalacetic transaminase, catalase, malondialdehyde), several gut bacterial indices (shannon, chaol, ACE, OTU5 abundance of proteobacterias) and abundance of hepatic PPARa mRNA in HI15.78 were remarkably lower than those in FM (P < 0.05), while content of crude lipid, gut firmicutes and hepatic Dgat2 mRNA were significantly lower than FM (P < 0.05). Results showed that HI improved growth performance and balance of gut bacteria of M. albus when supplemented at a rate below 15.78 %, but negative effects on lipid metabolism were observed when HI was supplemented at excessive levels.