Host-pathogen interaction unveiled by immune, oxidative stress, and cytokine expression analysis to experimental Saprolegnia parasitica infection in Nile tilapia.

The present study evaluated the pathogenicity, immunological, and oxidant/antioxidant responses against Saprolegnia parasitica (S. parasitica) infection in Nile tilapia (Oreochromis niloticus). Three groups of Nile tilapia were assigned as the control group (no zoospores exposure). The other two groups were challenged by Saprolegnia zoospores; one was used for sampling, and the other for mortality monitoring. The study lasted 3 weeks and was sampled at three point times at 1, 2, and 3 weeks. Results showed that S. parasitica zoospores were pathogenic to Nile tilapia, causing a cumulative mortality rate of 86.6%. Immunoglobulin M and C- reactive protein (IgM and CRP) levels showed a similar trend being significantly (P < 0.05, P < 0.001) higher in the infected group at weeks 1, 2, and 3, respectively, compared to the control group. Oxidant and antioxidant parameters in gills revealed that Malondialdehyde (MDA) level was significantly higher in the infected group compared to the control group. While catalase, glutathione peroxidase, and superoxide dismutase (CAT, GSH, and SOD) levels were significantly decreased in the infected group compared to the control group. Compared to the control, the tumor necrosis factor-α (TNF-α) gene was firmly upregulated in gill tissue at all-time points, particularly at day 14 post-infection. Meanwhile, Interleukin 1-ß (IL-1 ß) gene was significantly upregulated only at days 7 and 14 post-infection compared to control. Histopathological examination revealed destructive and degenerative changes in both skin and gills of experimentally infected Nile tilapia. Our findings suggest that Nile tilapia-S. parasitica infection model was successful in better understanding of pathogenicity and host (fish)-pathogen (oomycete) interactions, where the induced oxidative stress and upregulation of particular immune biomarkers in response to S. parasitica infection may play a crucial role in fish defense against oomycetes in fish.

Nannochloropsis oculata supplementation improves growth, immune response, intestinal integrity, and disease resistance of Nile Tilapia.

OBJECTIVE: The current study evaluated the potential roles of incorporating Nannochloropsis oculata into the diet of Nile Tilapia Oreochromis niloticus in an 8-week trial. METHODS: Dietary supplementation of N. oculata was tested at inclusion levels (0% [control], 5% [N5], and 10% [N1]) in triplicate. After the trial, comprehensive fish health indicators were evaluated. RESULT: N. oculata-supplemented feed had a stimulatory effect on fish body weight, where a significant increase in final weight and specific growth rate was observed in the N10 group compared to the control. Better feed conversion was observed at N5 and N10 compared to control. Organosomatic indices were elevated significantly in the N5 group compared to the N10 and control groups. Serum lysozyme activity was significantly increased in the N10 group compared to N5 and control groups. Levels of IgM were significantly higher in N10 compared to the control and N5 groups, with no significance between the latter. Amylase activity showed a significant enhancement in N10 compared to N5. Both levels of N. oculata preserved hepatic health and antioxidant status. Light and transmission electron microscopy showed that Nile Tilapia fed N. oculata at both levels enhanced intestinal immunity, integrity, and absorptive efficiency. The protecting effect of N. oculata was confirmed against Aeromonas hydrophila challenge, where cumulative mortalities were significantly decreased in N5 and N10 groups compared with the control and more in N10. CONCLUSION: This work confirmed the different beneficial roles of N. oculata dietary supplementation for a Nile Tilapia balanced diet.