The present study was conducted to assess the effect of replacing fish meal with whey protein concentrate (WPC) on the growth performance, histopathological condition of organs, economic efficiency, disease resistance to intraperitoneal inoculation of Aeromonas hydrophila, and the immune response of Oreochromis niloticus. The toxicity of WPC was tested by measuring the activity of caspase 3 as an indicator of cellular apoptosis. Oreochromis niloticus fingerlings with average initial weight 18.65 ± 0.05 gm/fish (n = 225) for a 10-week feeding trial. The fish were randomly allocated to five experimental groups, having five replacement percentages of fish meal with WPC: 0%, 13.8%, 27.7%, 41.6%, and 55.5% (WPC0, WPC13.8, WPC27.7, WPC41.6, and WPC55.5); zero percentage represented the control group. The results show that the fish fed WPC had the same growth performance as the WPC0. The total weight of bacterially challenged surviving fish increased linearly and quadratically (p ≤ 0.05) by increasing the replacement percentage of fish meal with WPC. The growth hormone, nitric oxide, IgM, complement 3, and lysozyme activity were seen to increase significantly in WPC27.7, especially after a bacterial challenge. The phagocytic percentage and phagocytic index increased significantly in WPC27.7, WPC41.6, and WPC55.5 groups. Histopathological examination of liver sections was badly affected by high replacement in WPC41.6–55.5. The activity of caspase 3 in the immunohistochemical stained sections of the intestine was increased significantly by increasing the inclusion level of WPC. Economically, the total return of the total surviving fish after the bacterial challenge was increased significantly by fish meal replacement with WPC. It could be concluded that WPC could replace the fish meal in Nile tilapia diets up to 27.7%, with improving the gut health, the total weight of survival fish, and immune status of fish challenged with A. hydrophila. High inclusion levels of WPC are not recommended in fish diets, since they negatively affected the intestinal and liver tissues and increased the level of cellular apoptosis, as indicated by the increased caspase 3 activity. Further researches are recommended to evaluate the effect of fish meal replacement with WPC on the histopathological examination of the kidney and to test the capacity of serum IgM to clot the bacteria used for the challenge.

In recent times, nutraceuticals have been used extensively to identify promising feed additives for the improvement of the aquaculture industry through the enhancement of growth and survival rates, potentiation of the immune responses, and fortification of the resistance against infectious bacterial diseases. In this study, Nile tilapia (Oreochromis niloticus) were fed with diets supplemented with quinoa seeds (QU) or prickly pear fruit peel (PP) at the dose levels of 10% or 20% of the diet. After 45 days of the feeding trial, the fish were exposed to Aeromonas sobria (A. sobria) challenge. The pre-challenge indices indicated that both supplements mediated a significant improvement in most of the estimated parameters, including survival rate, antioxidant status, hematological and immunological indices, and hepatoprotective potential. These effects were recorded in the groups fed with high doses of the supplements (20%). The least changes were observed in the QU₁₀-supplemented fish. In the spleen tissue, the TGF-β gene was upregulated in the PP₁₀-, PP₂₀- and QU₂₀-supplemented groups, while the expression of the IFN-γ gene remained unaffected in all the supplemented groups, except for the PP₂₀-supplemented group, which showed an upregulation. After the challenge with A. sobria, the relative survival percentage was improved by the supplementation of PP and QU, particularly in the PP₂₀-supplemented group, possibly via the promotion of immunological responses, hepatoprotective potency, and modulation of the studied genes. Moreover, the morphological structure of the tissues showed marked recovery. The findings suggest that Nile tilapia fed with different levels of PP peel and QU seeds, particularly at the level of 20%, enhanced the immune response in fish and improved their resistance against A. sobria infection.

Our goal in this study was to determine the effect of dietary supplementation with Moringa oleifera (M. oleifera), and Azadirachta indica (A. indica) leaves in mitigating the effects of chronic oxyfluorfen (OXY) toxicity on the health status, expressions of immune and antioxidant genes, and tissue morphological alterations in Oreochromis niloticus. In this study, we used 370 healthy O. niloticus (average weight = 25.35 ± 0.29 g). We used 70 fish to study the 96 h lethal concentration 50 (LC₅₀) of OXY. We assigned another 300 fish into six equal groups with five replicates (50 fish/group, 10 fish/replicate) to determine the chronic OXY toxicity for 60 days. The 96 h LC₅₀ of OXY for O. niloticus was 6.685 mg/L. Exposure to 1/10 96 h LC₅₀ of OXY (0.668 mg/L) had health impacts and pathological changes in the main tissues. In addition, the expressions of oxidant and immune genes were disrupted. Dietary supplementation with both M. oleifera and A. indica efficiently mitigated the toxic effects of OXY in the treated groups. Comparing the palliative efficiency of M. oleifera and A. indica, the results showed that M. oleifera was more potent in alleviating the toxic effects of OXY.

The Pseudomonas putida strain was primarily identified and tested in vitro against antibiotic sensitivity for several antibiotics using the disc diffusion method. This isolate was also tested against sensitivity to carvacrol oil (c) and formic acid (f). The genotyping of Pseudomonas spp. and virulotyping for P. putida isolate was carried out and verified by 16S rDNA-PCR amplification. Furthermore, we assessed the efficacy of carvacrol oil and formic acid in vivo for treatment of P. Putida infection. For the in vivo challenge, 180 fish (Nile tilapia, Oreochromis niloticus) were divided into six groups: (G1: control (unchallenged), G2: carvacrol prophylaxis (3 g/kg), G3: formic acid prophylaxis (5 mL/kg), G4: control positive (challenged), G5: carvacrol treatment (3 g/kg), and G6: formic acid treatment (5 mL/kg); 30 fish per group) with three replicates. Following the challenge, nitric oxide and lysozyme activity were measured as essential indicators for fish immunity. The antioxidant parameters including SOD and catalase were computed to reflect the antioxidant status. Furthermore, relative percent survival (RPS) and mortality percent were evaluated to indicate functional immunity. The findings of the antibiotic sensitivity test showed that ciprofloxacin exhibited the largest inhibition zone. Additionally, formic acid (f) displayed the greatest inhibition zone compared to carvacrol oil (c) and was more effective in stimulating the immune-antioxidant response compared to carvacrol oil. The tested exotoxin A (tox A), exoenzyme S (exo S), and the nan1 associated-virulence genes were identified in the P. putida isolate. Overall, the current study verified the virulence of P. putida and highlighted the promising role of dietary addition of formic acid for enhancing the immune-antioxidant indicators and for mitigating P. putida infection. Future studies could be devoted to this field.

Fish immunity is significantly impacted by waterborne metal intoxication. Nickel is a ubiquitous metal in aquatic bodies which badly impacts fish immune responses and survival. In the current research, we looked into the possible protective effects of essential oils of tea tree (TTO) and basil (BEO) against nickel exposure in Nile tilapia, or Oreochromis niloticus. To achieve this, 240 Nile tilapia (27.92 ± 0.22 g) were categorized into six groups for 45 days; three groups were fed on basal control, TTO, and BEO diets without Ni exposure. The other three groups were subjected to Ni at a level of 3.6 mg/L and fed on basal, TTO, and BEO diets. The outcomes showed a substantial decrease in the growth measures and survival % in the Ni-exposed fish. Oxidative stress (higher splenic malondialdehyde and lower splenic catalase, reduced glutathione, and superoxide dismutase), immune suppression (lower serum lysozyme, myeloperoxidase, and nitric oxide), and elevated serum cortisol levels were observed in the Ni-intoxicated group. The Ni-intoxicated group exhibited various pathological alterations detected in the intestinal tissue mainly inflammatory and necrotic changes, moreover, moderate depletion of lymphoid elements represented by necrotic lymphocytes in the splenic tissue. Ni-exposure induced endoplasmic reticulum stress through up-regulation of the splenic expression of protein kinase R-like endoplasmic reticulum kinase, activating transcription factor 6, CCAAT/enhancer-binding protein homologous protein, X-box binding protein 1, α-subunit of eukaryotic initiation factor 2, inositol-requiring kinase 1a, mitogen-activated protein kinase, c-JunN-terminal kinase, and binding protein for immunoglobulins. Feeding on the TTO and BEO diets improved the growth measures, survival, and antioxidant capacity. Immunomodulation, enhancement of the intestinal and splenic architecture, and relief of the endoplasmic reticulum stress condition were noticed when the Ni-intoxicant groups were fed on TTO and BEO diets. Overall, the effect of the TTO diet was more pronounced than the BEO diet in mitigating the negative consequences of Ni-intoxication in Nile tilapia. Dietary fortification of 0.1% TTO and/or 0.1% BEO is recommended during Ni exposure in aquaculture practices.