Application Of Housefly Maggot Meal Replacement Of Fish Meal In The Diet Of Litopenaeus Vannamei

In this research, the apparent digestibility of housefly maggot meal for juvenile white shrimp Litopenaeus vannamei was analyzed and then the growth performance, antioxidant and non-specific immune indexes, muscle quality, digestive enzyme activity, hepatopancreas function were investigated with different proportions of housefly maggot meal (HMM) replacement of fishmeal. Furthermore, the molecular biology technique was applied to evaluate effects of housefly maggot meal on the expression levels of a few protein metabolism relative genes in hepatopancreas. The contents and results are as follows:1. Apparent digestibility (AD) of housefly maggot meal for Litopenaeus vannamei. The ADs of dry matter, crude protein, crude lipid, energy and amino acids of HMM were evaluated for juvenile white shrimp Litopenaeus vannamei with an initial weight of (2.20±0.15) g, using a basal diet with yttrium oxide indicator. The results showed that ADs of dry matter, crude protein, crude lipid and energy of HMM were68.18%,83.34%,89.26%and75.38%, respectively. AD of total amino acids was86.56%and that of amino acids ranged from80.74%to92.31%, among which ADs of histidine, arginine, isoleucine and proline were higher than90%. The experimental results would provide reference data for the evaluation of nutritional value of HMM and exploiting artificial formulated feed for Litopenaeus vannamei.2. Effects of replacement of fish meal by housefly maggot meal of juvenile white shrimp(Litopenaeus vannamei). Six isonitrogenous and isoenergetic diets were formulated with0,20%,40%,60%,80%and100%replacement of fish meal with HMM on a protein basis.960juvenile shrimp with an average body weight of (0.56±0.03) g were randomly assigned to6groups. The shrimp were fed six diets for45days, respectively, named GO, G20, G40, G60, G80and G100. The results showed that there was no significant difference in weight gain rate (WGR) from G20to G60, while it was significantly decreased in G80and G100. Specific growth rate (SGR) of shrimp were significantly lower than that of the control group except for G40(P<0.05). FI (feed intake) in G100was significantly lower than other groups (P<0.05). Compared with the control group, there was no significant difference in feed conversion ratio (FCR), protein efficiency ratio (PER), protein deposition rate (PDR), hepatosomatic index (HSI) when the replacement levels were no more than60%, while FCR, HSI were significantly increased and PER, PDR were significantly decreased with increasing HMM replacement ratio. Condition factor (CF) and survival rate (SR) in HMM groups were higher than those in the control group to some extents. With HMM increasing, crude protein, calcium and total phosphorus content increased significantly and crude lipid content decreased (P <0.05), while dry matter and ash content were not significantly different (P>0.05). No significant difference was found among all the treatments in serum and hepatopancreas superoxide dismutase (SOD) activity, and serum malondialdehyde (MDA) content (P>0.05), MDA content in G80and G100was significantly higher than that of the control group (P<0.05). Serum phenoloxidase (PO) activity tended to increase first and then decrease, the highest value was observed in G20(P<0.05). Hepatopancreas alkaline phosphatase (AKP) activity decreased significantly with HMM increasing (P<0.05). In all the treatments, no significant difference was observed in serum total haemocyte count (THC), nitric oxide (NO) content, AKP activity and hepatopancreas PO activity and NO content (P>0.05). According to the growth performance parameters, antioxidant and non-specific immune indexes of juvenile L. vannamei, the replacement ratio of fish meal with HMM could be40%, and the maximum level should not exceed60%.3. Effects of replacement of fish meal with housefly maggot meal on muscle nutritional composition, amino acids and inosine monophosphate (IMP) content of juvenile Litopenaeus vannamei. After the above-mentioned alternative experiment finished, the muscle sample was prepared, the content of moisture, crude protein, crude lipid, ash, free and combinative amino acids as well as IMP in muscle was measured. The results showed that there was a positive correlation between crude protein and ash content in the muscle and the proportion HMM in the diet. The crude protein content in G100and the ash content in G80and G100were significantly higher than in the control group (P<0.05). HMM had no effect on moisture and crude lipid content (P>0.05). There was no difference in free delicious amino acid (DAA) content (glutamate and alanine only) and total free DAA among the groups. Total free essential amino acid (FEAA) content was significantly higher in G20to G100than in GO except for G40(P<0.05). Increasing amounts of HMM were associated with a significant increase in free arginine content (P<0.05) and a significant decrease in lysine content (P<0.05). The total free amino acid content was significantly higher in G20, but not in G40-G100, than in GO (P>0.05). The inclusion of HMM only had an effect on inosine monophosphate (IMP) content in G100(P<0.05). There was no significant difference in the content of combined DAA (aspartate, glutamate, glycine, alanine), EAA, or total amino acids in the muscle of groups fed HMM compared to the control (P>0.05). Overall, inclusion of HMM had no significant effect on the nutritional composition, EAA, DAA, and IMP content in the muscle, with the exception that the free arginine content increased significantly when HMM was substituted at levels less than60%.4. Effects of replacement of fish meal with housefly maggot meal on digestive enzyme, hepatopancreas histological structure and transaminase activity of Litopenaeus vannamei. After the above-mentioned alternative experiment finished, the protease, amylase, lipase activity in the hepatopancreas, stomach and intestine of L.vannamei was measured and hepatopancreas structure as well as transaminase activity was analyzed. The results showed that there was no significant difference in protease, amylase, lipase activity in the hepatopancreas, stomach and intestine of L.vannamei (P>0.05). The hepatopancreas histological structure was significantly affected by HMM. In G20and G40, tubules of hepatopancreas were well arranged and appeared as a star shape in the lumen, the basal membranes were undamaged and the amount of vacuoles in the epithelial cells increased, it appeared unknown substances in epithelial cells and they were increased in G60. When the replacement levels were more than80%, the unknown substances had greatly increased, the star shape of the lumen was partially lost. Tubules atrophy was observed and parts of the epithelial cells containing unknown substances were ruptured in G100. The ALT and AST activities of hepatopancreas in the HMM groups were lower than those in the control group to some extent, and there was no significant difference (P>0.05), while they were decreased significantly in serum(P<0.05). The results showed that the replacement of fish meal with HMM had no significant effect on protease, amylase and lipase activity in the hepatopancreas, stomach and intestine of L.vannamei, but it could result in pathological changes of histological structure, and HMM replacement level should not be over60%.5. Effects of replacement of fish meal with housefly maggot meal on the expression levels of hepatopancreas cathepsin B and ribosomal protein L8of Litopenaeus vannamei. After the above-mentioned alternative experiment finished, the hepatopancreas sample was prepared, and the hepatopancreas cathepsin B (CAT B) and ribosomal protein L8(RPL8) expression levels among all groups were analyzed. The results showed that HMM had a significant effect on hepatopancreas CAT B expression levels (P<0.05). Expression levels in HMM substitution groups were higher than that of the control group, among which the CAT B expression levels in G40and G100showed significant difference (P<0.05), and it was the highest in G100. Compared to the control group, the RPL8expression levels were higher in HMM groups, and they were up-regulated by21%-29%, but there was no significant difference among all the treatments (P>0.05).