Effect of kelp powder on the resistance of Aeromonas hydrophila in the gut of hybrid snakeheads (Channa maculata ♀ × Channa argus ♂).

To assess the level of oxidative stress, expression of immune-related genes, histomorphology, and changes in the intestinal tract of hybrid snakeheads(Channa maculata ♀ × Channa argus ♂) under stress from kelp powder in place of flour against Aeromonas hydrophila. We set up experimental diets: a control (C) diet of 20% flour, an experimental (MR) diet of 10% kelp powder and 10% flour, and an experimental (FR) diet of 0% starch and 15% kelp powder. The experimental fish in each group were infected with Aeromonas hydrophila after 60 days of feeding. For this experiment, some of the experimental fish in group C were injected with PBS as a negative control group (PBS). The results showed that the C group had significantly higher SOD, CAT, and T-AOC activity and expression of TAK1, IKKß, IL-1ß, and TNF-α genes in the MyD88 pathway than the PBS group. CAT activity and the expression of TAK1, IL-1ß and TNF-α genes in the MyD88 pathway were significantly lower in the MR group than in the C group. Furthermore, the number of goblet cells in the MR group was significantly higher than in the C group. Furthermore, microorganisms such as Bacteroidota and Actinobacteriota were significantly lower in the C group than in the PBS and FR groups, as were beneficial bacteria such as Clostridium_sensu_stricto_1 and Sphingomonas. Replacing flour with kelp powder increases hybrid snakehead gut resistance to Aeromonas hydrophila.

Vitamin E performs antioxidant effect via PAP retrograde signaling pathway in Nile tilapia (Oreochromis niloticus).

PAP (3'-phosphoadenosine 5'-phosphate) is a ubiquitous phosphoric acid and a natural inhibitor of the XRN (5'-3'exoribonuclease) family. It was proved to enter the nucleus through the retrograde signaling pathway and inhibit XRN2 to prevent the degradation of miRNA precursors, thus promoting the anti-oxidation miRNA level in Arabidopsis thaliana. Vitamin E (tocopherol) was proved to promote the accumulation of PAP in the plant, which facilitates PAP into the nucleus to accomplish its antioxidant function. However, the relationship between VE and PAP in animals is unclear. To identify the relationship between VE and PAP and to uncover the function of PAP in fish, we investigated the performance of VE and PAP in Nile tilapia by comparing the antioxidant indicators (SOD, GSH-Px, and CAT), the Keap1-Nrf2 signaling pathway, and the miRNA expression profiles. Results showed that the antioxidant effect of VE and PAP showed similar character either in tilapia liver or in serum: the activities of GSH-Px and CAT of both groups were significantly increased (P < 0.05); the SOD activity of the VE group was significantly increased (P < 0.05), and although the result of the PAP group was not so significant (P > 0.05), PAP improved the SOD level, too. The two groups also showed similar character in the tilapia liver; both did not significantly increase the liver δ-VE content (P > 0.05). However, VE significantly increased the content of α-VE and γ-VE (P < 0.05), while the PAP group was insignificant (P > 0.05). Feed with VE and intraperitoneal injection of PAPs reagent both increased the PAP content in the liver of tilapia, and the effect of the VE group was more significant (P < 0.05) than that of the PAP group (P > 0.05). Both groups reduced the expression of Keap1 and Cullin3 genes and improved the level of HO-1 gene expression, with the improved miRNA level of Nrf2. As a logical result, they decreased the expression of XRN1 and XRN2. By profile sequencing, we further identified some antioxidant closely related miRNAs shared in the VE and PAP groups, including miR-30, miR-24, miR-19b, and miR-100. By comparing the regulating mechanism of VE and PAP of feed supply and intraperitoneal injection, we proved that VE and PAP were closely related in fish; VE promoted the gathering of PAP. The latter retrograded into the nucleus of the fish liver to inhibit the expression of XRN genes and to up-regulate antioxidant miRNA levels as it does in plants. Only the PAP can accomplish the antioxidant activities, while VE promotes the process. Our study laid the foundation for the application of PAP as a new antioxidant agent in fish farming and benefit a further understanding of the VE antioxidant function in fish.