Effect of fatty acid-enriched black soldier fly larvae meal combined with chitinase on the metabolic processes of Nile tilapia.

The aim of this study is to determine to what extent the addition of chitinase to black soldier fly (BSF) larval meal enriched or not with long-chain PUFA (LC-PUFA) could improve growth, protein digestion processes and gut microbial composition in Nile tilapia. Two different types of BSF meal were produced, in which larvae were reared on substrates formulated with vegetable culture substrate (VGS) or marine fish offal substrate (FOS). The BSF raised on VGS was enriched in α-linolenic acid (ALA), while that raised on FOS was enriched in ALA + EPA + DHA. Six BSF-based diets, enriched or not with chitinase, were formulated and compared with a control diet based on fishmeal and fish oil (FMFO). Two doses (D) of chitinase from Aspergillus niger (2 g and 5 g/kg feed) were added to the BSF larval diets (VGD0 and FOD0) to obtain four additional diets: VGD2, VGD5, FOD2 and FOD5. After 53 d of feeding, results showed that the BSF/FOS-based diets induced feed utilisation, protein efficiency and digestibility, as well as growth comparable to the FMFO control diet, but better than the BSF/VGS-based diets. The supplementation of chitinase to BSF/FOS increased in fish intestine the relative abundance of beneficial microbiota such as those of the Bacillaceae family. The results showed that LC-PUFA-enriched BSF meal associated with chitinase could be used as an effective alternative to fishmeal in order to improve protein digestion processes, beneficial microbiota and ultimately fish growth rate.

Intestinal histopathology and immune responses following Escherichia coli lipopolysaccharide challenge in Nile tilapia fed enriched black soldier fly larval (BSF) meal supplemented with chitinase.

This study aimed to determine to what extend the addition of chitinase to black soldier fly larvae (BSF) meals enriched with either PUFA or LC-PUFA could improve the gut health of Nile tilapia and increase its immune status. Two types of BSF meals enriched with either α-linolenic acid (ALA) or ALA + eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) were produced using BSF larvae cultured on vegetable substrates (VGS) or fish offal substrates (FOS), respectively. Seven diets were formulated: a control FMFO diet and two other control diets VGD0 vs FOD0 containing the meals of each type of BSF meal as total replacement for fishmeal (FM) and fish oil (FO), as well as four diets supplemented with chitinase. Two doses of commercial chitinase from Aspergillus niger (2 g/kg and 5 g/kg of feed) were supplemented to the other diets VGD0 and FOD0 to formulate VGD2, VGD5, FOD2 and FOD5. After 53 days of feeding, FOD5 diet induced a similar growth performance as the FMFO control diet, while a significant decrease of growth was observed for the other BSF larval-based diets. BSF/FOS meal led to higher SGR of fish than BSF/VGS, as for the FOD5 compared to VGD5. At day 53, lysozyme values showed an increasing trend in fish fed all the BSF-based diets, especially those fed the VGD5. After the Escherichia coli lipopolysaccharide (LPS) injection (day 54), the same increasing trend was observed in lysozyme activity, and modulation was observed only in the VGD5 fish. ACH50 activity was reduced by the BSF-based diets except for the FOD5 diet at day 53, and LPS modulation was only observed for the VGS-chitinase-based diets at day 54. Peroxidase activity and total immunoglobulin (Igs) blood level were not affected by substrate, chitinase dose or LPS injection. At day 53, the low or high dose of chitinase increased the expressions of tlr2, il-1ß and il-6 genes in the head kidney of fish fed the BSF/VGS diets compared to those fed the VGD0 or FMFO control diets. At day 54 after LPS injection, the high dose of chitinase decreased the expressions of tlr5 gene in the spleen and mhcII-α gene in the head kidney of fish fed FOD5 diets compared to those fed FOD0 diets. BSF/VGS but not BSF/FOS based diets increased fish sub-epithelial mucosa (SM) and lamina propria (LP) thickness and the number of goblet cells (GC) in fish, but dietary chitinase seemed to prevent some of these effects, especially at low dose. Results showed that chitinase supplementation of 5 g/kg of chitinase to a BSF-based diet enriched with LC-PUFA improved growth, prevented histological changes in the proximal intestine and enhanced some innate immune functions of Nile tilapia without any clear booster effect after challenge with E. coli LPS.

Immune responses and acute inflammation in common carp Cyprinus carpio injected by E.coli lipopolysaccharide (LPS) as affected by dietary oils.

Eicosanoids, resolvins, and lipoxins formed from long-chain polyunsaturated fatty acids (LC-PUFAs) are the main lipid mediators in the inflammatory processes explaining the influence of dietary lipid sources on the immune system. The current study aimed to determine the effects of dietary plant oils instead of fish oil or LC-PUFA supplementation in these oils on fish immune and inflammatory responses under normal and LPS-stimulated conditions. Six iso-nitrogenous (ranging from 30.4 to 31.1%) and iso-lipidic (from 11.2 to 11.6%) diets were formulated using three oil sources: cod liver oil (CLO, as fish oil control); linseed oil (LO, rich in α-linolenic acid, ALA); sesame oil (SO, rich in linoleic acid, LA); a blend of LO and SO (SLO, v:v 1:1); and two pure plant oil diets supplemented with docosahexaenoic acid, DHA (SO + DHA, SOD) or arachidonic acid, ARA (LO + ARA, LOA). Fish were fed the experimental diets to satiation for 42 days. On day 43, they were injected with E.coli lipopolysaccharide (LPS) at 100 µg/fish. Fish plasma and tissues such as head kidney and liver were collected on day 42 and one day after LPS injection (day 44) for humoral immune variables and gene expression analyses, respectively. After 42 days of feeding, no influences of dietary oils were found on fish survival, growth, feed utilization, and humoral immune responses. On the other hand, LPS injection significantly stimulated immune responses and induced an acute inflammation in common carp through an increase of the complement activity and the up-regulation of genes involved in the innate immune system (c2), pro-inflammatory response (tlr-4, tnf-α, il-1, il-6, il-8, and cxc), eicosanoid metabolism (pla2, cox-1, 5-lox, and pge2), and anti-inflammatory response (tgf-ß1 and nf-fki). Further, the expression of hsp70 was stimulated by LPS injection. The effects of dietary oil sources were observed after LPS injection, with a significant modification in the expression of almost all candidate genes. The highest pro-inflammatory responses induced by LPS were observed in CLO-fed fish while the mixture of plant oils (SLO) and LC-PUFA-supplemented diets induced significantly higher modulations in anti-inflammatory responses (il-10 and nf-kbi), general stress status (hsp70), and cytoprotection (gpx-1) compared to fish oil control and other pure plant oil groups. In conclusion, the immune response of common carp has been modified by the dietary fat sources. The fish oil-based diet supported an increase of the pro-inflammatory responses while the mixture of plant oil or LC-PUFA supplemented diets improved the anti-inflammatory responses and cytoprotection.