Effect of biological additives on Japanese eel (Anguilla japonica) growth performance, digestive enzymes activity and immunology.

Japanese eel (Anguilla japonica) has become a commercially important fish species all over the world. High-density aquaculture has led to congestion and contributed to bacterial infection outbreaks that have caused high mortality. Therefore a 56-days feeding trial was conducted to determine the effects of dietary Bacillus amyloliquefaciens (GB-9) and Yarrowia lipolytica lipase2 (YLL2) on growth performance, digestive enzymes activity, innate immunity and resistance to pathogens of A. japonica. Fish growth performance was significantly affected by dietary YLL2 supplementation but not by GB-9. Fish fed diets with YLL2 at 2.0 g/kg diet in combination of high and low levels of GB-9 (5.0 g/kg and 2.0 g/kg) produced the highest growth. For digestive enzyme, lipase and trypsin activities was promoted by dietary containing YLL2, while amylase activities was increased by dietary containing YLL2, GB-9 single or combination. For innate immunity, the mucus lysozyme activity, leukocytes phagocytosis activity and reactive oxygen species level of skin, peroxidase and lysozyme activity of serum were enhanced in fish fed with GB-9 compared to those in control group (p < 0.05). The highest resistance to Vibrio anguillarum and Aeromonas hydrophila was determined in fish fed with 5.0 g kg-1 GB-9 + 2.0 g/kg YLL2. This study demonstrated that GB-9 and YLL2 enhanced non-specific immune defense system of A. japonica, providing them with higher resistance to pathogens. The present results suggested that the combination of these supplements could be considered as potential biological additives for aquaculture farmed fish.

Effects of Bacillus amyloliquefaciens and Yarrowia lipolytica lipase 2 on immunology and growth performance of Hybrid sturgeon.

A 12-weeks feeding trial was performed to investigate the possible effects of supplementation of Hybrid sturgeon diet with Bacillus amyloliquefaciens (GB-9) and Yarrowia lipolytica lipase2 (YLL2) single or combined on immune response and growth performance of Hybrid sturgeon (Acipenser schrenkii ♂and Acipenser baeri ♀). For this aim, Hybrid sturgeons were fed with four experimental diets namely: Diet 1 (0-control), Diet 2 (5.0 g/kg GB-9), Diet 3 (4.0 g/kg YLL2), and Diet 4 (5.0 g/kg GB-9 + 4.0 g/kg YLL2), respectively. After fed with varied diets, growth performance, mucosal immune response, leukocytes immune response and serum immunological response were measured. The results indicated that supplementations of GB-9 + YLL2 resulted in a significant increase in final weight, Docosahexaenoic acid (DHA) and Eicosapentenoic acid (EPA) concentration, compared with that of control (p < 0.05). For innate immunity, the results showed that skin mucus lysozyme activity, leukocytes phagocytosis activity and reactive oxygen species level, and serum alternative complement pathway activity, peroxidase and lysozyme activity were significantly higher in supplemented groups compared to the control (p < 0.05). The highest values were recorded in fish fed both YLL2 and GB-9 with respect to the individual application. The present results suggested that the combination of these supplementation could be considered as potential feed-additives for aquaculture farmed fish.

Transcriptome and 16S rRNA analysis revealed the response of largemouth bass (Micropterus salmoides) to Rhabdovirus infection.

To better understand the response of largemouth bass (Micropterus salmoides) to Micropterus salmoides rhabdovirus (MSRV) infection, we investigated the intestinal bacterial flora and transcriptome profile of fish at 72 hours post-infection (hpi). Total of 1574 differentially expressed genes (DEGs) were identified in largemouth bass spleen following MSRV infection, including 573 upregulated and 1001 downregulated genes. KEGG and GO enrichment analysis revealed that upregulated genes were enriched in certain antiviral related signaling pathway, including NOD-like receptor (NLR), RIG-I like receptors (RLR) and regulation of the interferon (IFN)-γ-mediated signaling pathway, whereas some immune-related DEGs enriched in focal adhesion (FA) and ECM-receptor interaction(ECM-RI) were downregulated, as well as genes associated with metabolic processes, such as peroxisome proliferator-activated receptors (PPAR), adipocytokine signaling pathway, Glycerolipid and Retinol metabolism. Furthermore, the principal component analysis (PCA) and phylogenetic analysis revealed that MSRV infection significantly affected the microbiota of largemouth bass intestine; the LEfSe analysis showed that relative abundances of Streptococcus were significantly increased, while the content of Akkermansia, Enterococcus and Lactobacillus were remarkably decreased in the fish intestine following MSRV infection. Additionally, a high correlation was determined between the expressions of interferon-related upregulated genes and the relative abundance of Streptococcus by redundancy analysis (RDA). These results collectively illustrated that intestinal microbiota composition might be associated with the immune-related gene expression in largemouth bass in response to MSRV infection.