Infection dynamics of Shewanella spp. in Nile tilapia under varied water temperatures: A hematological, biochemical, antioxidant-immune analysis, and histopathological alterations.

In aquaculture, fluctuating water temperatures can act as a potent stressor, influencing the virulence and transmission dynamics of pathogenic bacteria, potentially triggering outbreaks and impacting fish health. The purpose of this work was to examine the impact of Shewanella spp. infection on hematological, biochemical, and antioxidant-immune parameters of Nile tilapia (Oreochromis niloticus) under different water temperatures. For this purpose, 180 fish were divided into 6 groups in triplicate (30 fish per group; 10 fish per replicate). Group 1 (G1), G2, and G3 were reared at varying water temperatures (22 °C, 28 °C, and 31 °C, respectively) without infection. While G4, G5, and G6 were IP-injected with 0.2 mL of Shewanella spp. (0.14 × 105) and reared at 22 °C, 28 °C, and 31 °C, respectively. Shewanella spp. infection induced significant lowering (p < 0.05) in hematological parameters (red and white blood cells, hemoglobin, and packed cell volume%) and immune-antioxidant responses (phagocytic activity%, phagocytic index, lysozyme, nitric oxide), total antioxidant capacity, catalase, and reduced glutathione, especially at 22 °C. Moreover, a significant increase (p < 0.05) in the hepato-renal function indicators (alanine aminotransferase, aspartate aminotransferase, urea, and creatinine), stress biomarkers (glucose and cortisol), malondialdehyde, and pro-inflammatory cytokines (interleukin-1ß and tumor necrosis factor-α) were the consequences of the Shewanella spp. infection, especially at 22 °C. The Shewanella spp. infection exhibited marked histopathological changes in the hepatic and renal tissues. Worthily, Shewanella spp. can cause detrimental alterations in Nile tilapia's hematological, biochemical, and antioxidant-immune parameters at various water temperatures, but the major detrimental changes were observed at a water temperature of 22 °C. Consequently, we can conclude that the infection dynamics of Shewanella spp. are exaggerated at 22 °C. These outcomes could help in understanding the nature of such an infection in Nile tilapia.

Implications of ammonia stress for the pathogenicity of Shewanella spp. in Oreochromis niloticus: effects on hematological, biochemical, immunological, and histopathological parameters.

Environmental stressors (such as ammonia) in aquaculture could increase the risk of pathogenicity, posing a more severe threat to farmed fish. The aim of this study was to investigate the effects of ammonia stress on the pathogenicity of Shewanella spp. in Oreochromis niloticus. First, a 96-hour static test was used to determine the median lethal concentration (LC50) of unionized ammonia to Nile tilapia. After 96 h of exposure, the Un-ionized ammonia (UIA) LC50 was estimated to be 4.26 mg/L. Second, an experiment was conducted to test the effect of unionized ammonia stress on the pathogenicity of Shewanella spp. in O. niloticus for 30 days. A study involved 180 fish divided into six groups, with the first group serving as a control. The second group (AMN1/10) and the third group (AMN1/20) were not challenged and were exposed to 1/10 (0.42 mg/L) and 1/20 (0.21 mg/L) of the 96-hour LC50 of UIA, respectively. Then 0.2 mL (0.14 × 105) of Shewanella spp. was intraperitoneally injected into the fourth (SH), fifth (SH + AMN1/10), and sixth (SH + AMN1/20) groups, which were subjected to 0, 1/10 (0.42 mg/L), and 1/20 (0.21 mg/L) of the 96-hour LC50 of UIA, respectively. The survival rate, hematological indices, immunological parameters, and antioxidant activity of the fish significantly decreased when they were exposed to ammonia and Shewanella infection separately or together. Histopathological changes were also observed in the kidney and liver. Furthermore, both individual and combined exposures significantly altered renal and hepatic function, with notable increases in glucose and cortisol levels, as well as in the expression of proinflammatory cytokine genes (TNF-α and IL-1ß). However, the detrimental effects of co-exposure to ammonia stress and Shewanella infection were greater than those of separate exposures. As a result, we may say that increased ammonia concentrations enhance the infection of Shewanella spp. These findings could contribute to a better understanding of Shewanella infection in Nile tilapia.

ß-1,3-glucan improved the health and immunity of juvenile African catfish (Clarias gariepinus) and neutralized the histological changes caused by lead and fipronil pollutants.

BACKGROUND: Water pollutants cause adverse effects in aquatic ecosystems. The immunomodulatory and mitigating effects of dietary 1,3-glucan on fipronil and lead-induced intoxication in African catfish (Clarias gariepinus) were investigated. Two hundred forty catfish were randomly divided into four equal groups: those in the first group were fed basic diet and served as controls; those in the second group were supplemented with ß-1,3-glucan (0.1%); those in the third group were exposed to combination of lead nitrate at 0.041 mg/L (1/10 96 h LC50) and fipronil at 2.8 mg/l (1/10 96 h LC50); and those in the fourth group were exposed to combination of fipronil, lead, and ß-1,3-glucan. The health status, haematological, immunological, and histological changes were all evaluated. RESULT: Swelling on the dorsolateral side, spinal column deviation, sluggish movement, skin bleaching, excessive mucus secretion, significant variations in blood indices-related measures, and a 45% death rate were observed in the third group. There was a significant reduction in interleukin-1 (IL-1) and interleukin-6 (IL-6) and immunoglobulin M (IgM) concentrations, as well as decrease in their corresponding gene expression, indicating that fipronil and lead had immunosuppressive activity. Severe catarrhal enteritis and mucinous degeneration of the lining epithelium, and notable depletion of white pulp, congested red pulp and hemosiderosis were common pathological findings in the spleen. ß-1,3-glucan alone or in combination with fipronil and lead provoked physical activity, blood indices, with elevations in IL-1ß, IL-2, IL-6, and IgM concentrations, as well as up-regulation in their genes' expression in splenic tissues, when compared to the third group. The spleen and intestine had normal histological architecture with 5% mortalities. There were no fish deaths in the ß-1,3-glucan-alone or control groups. CONCLUSION: The use of ß-1,3-glucan (0.1%) as dietary supplement could be implemented to protect against the toxic effects of fipronil and lead toxicity by improving the health and immunological parameters of intoxicated catfish.

Nephroprotective and antioxidant significance of selenium and α-tocopherol on lead acetate-induced toxicity of Nile Tilapia (Oreochromis niloticus).

The kidney plays an important physiological function, maintaining the osmoregulation and electrolyte balance of Nile tilapia (Oreochromis niloticus). Selenium and α-tocopherol (α-toc) are potent antioxidants, which improve the aquaculture health. In this study, we tested the potential ability of selenium and α-toc to alleviate the oxidative stress in the kidney induced by lead toxicity. Two hundred and twenty-five O. niloticus were divided into five groups. The control group received a basal diet. Lead nephrotoxicity was induced by daily application of 73.40 mg lead acetate/liter water for up to 10 weeks. Selenium and α-tocopherol were given 1 week before lead intoxication. Selenium was administered as sodium selenite, 4 mg/kg dry diet. Alpha-tocopherol acetate was administered as α-toc, 200 mg/kg dry diet. The last group received a mixture of selenium and α-toc in diet. Fish treated with selenium and/or α-toc (groups III-V) showed an amelioration of the adverse effects of lead toxicity and significant improvement in serum electrolytes (calcium, inorganic phosphate, and magnesium) and creatinine level compared with the positive control group (P ≤ 0.05). Treated groups showed significant decrease in superoxide dismutase (SOD) and reduced glutathione (GSH) activity with significant increase in malondialdehyde (MDA; P ≤ 0.05). It could be concluded that selenium and α-toc have a potential antioxidant effect and have the ability to improve the kidney function after lead intoxication of O. niloticus.

Effect of dietary intervention with Capsicum annuum extract on growth performance, physiological status, innate immune response, and related gene expression in Nile tilapia.

The red pepper (Capsicum annuum) has gained great attention recently because of its biological and pharmacological characteristics. The present approach aimed to evaluate the effects of C. annuum alcoholic extract (CAE) supplementation on Nile tilapia (Oreochromis niloticus) growth performance, physiological status, some metabolic, immune, and regulatory genes expression, and resistance against Streptococcus agalactiae infection. Fish (22.26 ± 0.19 g) were assigned to four treatments (five replicates, each with 10 fish replicate-1) and fed tested diets for 60 days. The experimental diets were supplemented with CAE at 0, 0.4, 0.8, and 1.6 g kg-1, expressed as CAE0, CAE0.4, CAE0.8, and CAE1.6, respectively. The findings exhibited that CAE dietary supplementation improved growth performance, feed utilization, elevated growth hormone level, and digestive enzyme activities (amylase and protease), and lowered leptin hormone in a level-dependent manner. Boosting the mRNA expression of the transporter proteins (solute carrier family 15 member 2 and solute carrier family 26 member 6) and insulin-like growth factor-1 genes with a decrease in the myostatin gene expression was noticed in the CAE-fed groups. The innate immune (serum bactericidal activity %, complement 3, and phagocytic activity %) and antioxidant (glutathione peroxidase and total antioxidant capacity) parameters were significantly (p < 0.05) improved, and the serum malondialdehyde level was significantly decreased by CAE dietary inclusion. A marked upregulation in the mRNA expression of interleukins (il-1ß, il-6, il-8, and il-10), transforming growth factor-ß, glutathione peroxidase, and glutathione synthetase genes were observed in CAE-fed groups. Dietary CAE decreased the cumulative mortalities after the challenge with S. agalactiae by 20, 13.33, and 10% in CAE0.4, CAE0.8, and CAE1.6, respectively, compared to the control (40%). Overall, dietary supplementation with CAE could improve growth performance and physiological status, and modulate the expression of several regulatory genes in Nile tilapia. The recommended level of CAE is 1.6 g kg-1 to augment growth and health status.

Chitosan neem nanocapsule enhances immunity and disease resistance in nile tilapia (Oreochromis niloticus).

Finding eco-friendly alternatives for antibiotics in treating bacterial diseases affecting the aquaculture sector is essential. Herbal plants are promising alternatives, especially when combined with nanomaterials. Neem (Azadirachta indica) leaves extract was synthesized using a chitosan nanocapsule. Chitosan neem nanocapsule (CNNC) was tested in-vitro and in-vivo against the Aeromonas sobria (A. sobria) challenge in Nile tilapia. A preliminary experiment with 120 Nile tilapia was conducted to determine the therapeutic dose of CNNC, which was established to be 1 mg/L. A treatment study was applied for seven days using 200 fish categorized into four groups (10 fish/replicate: 50 fish/group). The first (control) and second (CNNC) groups were treated with 0 and 1 mg/L CNNC in water without being challenged. The third (A. sobria) and fourth (CNNC + A. sobria) groups were treated with 0 and 1 mg/L CNNC, respectively, and challenged with A. sobria (1 × 107 CFU/mL). Interestingly, CNNC had an in-vitro antibacterial activity against A. sobria; the minimum inhibitory concentration and minimum bactericidal concentration of CNNC against A. sobria were 6.25 and 12.5 mg/mL, respectively. A. sobria challenge caused behavioral alterations, skin hemorrhage, fin rot, and reduced survivability (60%). The infected fish suffered a noticeable elevation in the malondialdehyde level and hepato-renal function markers (aspartate aminotransferase, alanine aminotransferase, and creatinine). Moreover, a clear depletion in the level of the antioxidant and immune indicators (catalase, reduced glutathione, lysozymes, nitric oxide, and complement 3) was obvious in the A. sobria group. Treatment of the A. sobria-challenged fish with 1 mg/L CNNC recovered these parameters and enhanced fish survivability. Overall, CNNC can be used as a new versatile tool at 1 mg/L as a water treatment for combating the A. sobria challenge for sustainable aquaculture production.

Endosulfan toxicity in Nile tilapia (Oreochromis niloticus) and the use of lycopene as an ameliorative agent.

OBJECTIVES: Endosulfan is a broad-spectrum organochlorine insecticide that has been commercially in use for decades to control insect pests and has been found to pollute the aquatic environment. The current study was carried out to investigate the toxic effects of endosulfan, an organochlorine pesticide, on Nile tilapia (Oreochromis niloticus), a freshwater fish, and the alleviating effects of lycopene on the induced toxicity. METHODS: Four treatment groups of fish were investigated (3 replicates of 15 fish for each group): (1) a control group, (2) a group exposed to endosulfan, (3) a group that was fed on a basal diet supplemented with lycopene, and (4) a group that was fed on a basal diet supplemented with lycopene and exposed to endosulfan. The experiment was carried out over a 4-week period. RESULTS: Endosulfan negatively affected liver function, including liver enzymes and plasma proteins. Endosulfan affected blood parameters of fish and reduced the counts of red blood cells (RBCs) and white blood cells (WBCs), as well as affected immunological parameters. Endosulfan caused oxidative stress, as it decreased the values of antioxidants catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX), and glutathione (GSH), and increased the level of lipid peroxide malondialdehyde (MDA). Additionally, endosulfan increased cytochrome P450 (CYP450) levels, while it decreased glutathione S-transferase (GST) mRNA transcript levels and distorted the normal histological structure of the liver, gills, and spleen of affected fish. Conversely, lycopene partially restored the aforementioned parameters when administered concomitantly with endosulfan. CONCLUSION: The results showed the beneficial effects of supplementing fish diets with lycopene as a natural antioxidant for ameliorating the toxicity caused by endosulfan.