Aquaculture is the farming of aquatic organisms like fish, crustaceans, mollusks, and aquatic plants, which has become a crucial source of protein and income. However, bacterial infections pose a significant challenge to the aquaculture industry and traditional treatments, such as antibiotics and chemicals, have limitations and environmental concerns. Disease prevention and control measures, such as the use of probiotics, vaccines, and biosecurity measures, are essential for the sustainable development of the aquaculture industry. Further research is also needed to develop more effective and sustainable strategies for the prevention and control of bacterial fish pathogens in aquaculture, where alternative treatments such as herbal extracts, essential oils, and probiotics require further investigation for efficacy and safety. Microalgae, particularly Chlorella, have potential applications in various industries such as biofuels, pharmaceuticals, and wastewater treatment. However, their large-scale production and commercialization face challenges. Safety of Chlorella to fish is a crucial issue that requires careful evaluation, with hematology being an essential tool to assess its effects on fish health and physiology. Studies show that Chlorella is safe for fish and does not have adverse effects on growth, survival, or immune system function. Chlorella is a safe and sustainable option for aquaculture, free from harmful chemicals and antibiotics. The Green Water System utilizes Chlorella as a natural filter and nutrient recycler, improving water quality and providing a well-balanced diet for aquatic animals. This eco-friendly approach also enhances fish immune systems, growth rates, and survival rates. The scientometric review shows significant research activity, with Chang JS being a prominent author and People’s R China and the Chinese Academy of Sciences leading in contributions. The use of Chlorella shows promise as an alternative treatment for bacterial fish pathogens in aquaculture due to its antibacterial properties, safety, and sustainability. However, challenges such as cost-effectiveness and standardization need to be addressed for successful implementation in the aquaculture industry.

The present study investigated the effect of Chlorella vulgaris on growth performance, feed consumption, body composition, and immune response of white shrimp (Litopenaeus vannamei) against Vibrio parahaemolyticus infection. Shrimps (4.00 ± 0.04 g) were divided into five groups (3 replicates/20 each) in 15 hapa (1 m³) and cultured for 56 days with five C. vulgaris experimented diets at five different concentrations (0, 15, 20, 25, and 30 g/kg feed). Growth performance, feed utilization, biomass, and body composition (protein, lipid, and ash) were analyzed and revealed significant increase (P < 0.05) in shrimp fed the high C. vulgaris diet. Additionally, the survival rate of shrimp in all experimental feeds was improved, but was not significant. Shrimp fed with C. vulgaris at different concentrations showed significantly (P < 0.05) higher antioxidant activity. The study showed that shrimp fed with a concentration of 30 g/kg C. vulgaris in the diet showed significantly (P < 0.05) highest disease resistance against the pathogen tested. Hence, dietary C. vulgaris might be used to improve growth performance, feed utilization, body composition, and immune biomarker responses, leading to disease resistance in cultured shrimp.

The objective of this study was to explore the effects of black seed (Nigella sativa) and AQUA-IMMUNOPROTECT® on growth, feed utilization, serum constituents, and disease resistance against vibriosis in gilthead sea bream juveniles. The research involved three groups: T_C (control) received a basal diet, T_SI (received a basal diet with 2% AQUA-IMMUNOPROTECT®), and T_NS (received a basal diet with 2% N. sativa). The experiment period extended for 2 months. Results revealed a significant rise in erythrogram (RBCs, HB, and PCV %), leucogram (total differential leucocytic count), serum total protein, and globulin in gilthead sea bream treated with 2% Nigella sativa supplemented diets after an 8-week trial. No substantial variations were found in liver enzymes, urea, uric acid, and creatinine between the groups. Respiratory burst activity was notably greater in the N. sativa group after 2 months of feeding compared to the other groups. In the experimental challenge, the control group experienced higher mortality rates than the other groups following an IP injection of V. harveyi at a dose of 10⁶ CFU per 0.5 ml/fish (10⁶ fish/challenge). Overall, the findings of this research indicate that N. sativa can enhance non-specific immunity and minimize susceptibility and pathogenicity to V. harveyi in gilthead sea bream.

: This research was carried out to study the bacterial etiology of ulcerative syndrome in Nile tilapia (Oreochromis niloticus) and its associated environmental stressors. A total of 90 live and moribund Nile tilapia showing signs of ulcerative dermatitis were collected from various fish ponds in El-Sharkia Province, Egypt, during the summer seasons from June 2019 to August 2020. Collected fish were subjected to full clinical and postmortem investigation followed by bacteriological and molecular identification of the bacterial agents as well as histopathological examinations. Moreover, water samples from the fish sampling sites were collected and analyzed physiochemically and microbiologically. Furthermore, the pathogenicity of the isolated strains was assessed by challenging apparently healthy Nile tilapia to determine the LD₅₀. Clinically, the examined fish exhibited ulcerative dermatitis as focal or fused large ulcers surrounded by red zones of hemorrhages at different body parts. Bacteriologically, Aeromonas veronii biovar sobria and A. caviae were isolated and identified. Moreover, 16S rRNA gene sequencing and phylogenetic analysis verified the identity of these species. Antibiogram profiling of the recovered Aeromonas sp. isolates showed complete resistance to ampicillin, with high susceptibility to gentamycin, trimethoprim/sulphamethoxazole, and erythromycin. Histopathological examination of the affected fish revealed epidermal necrosis with dermal edema and an influx of inflammatory cells into the dermis and hypodermis. The LD₅₀ of A. veronii biovar sobria and A. caviae was estimated as 1.5 × 10⁷ and 1.5 × 10⁸ CFU/fish; respectively. The water temperature and ammonia concentrations recorded a significant rise (P ≤ 0.05) in July and August compared to June; however, the highest pH levels were recorded during August, followed by July. Also, the total bacterial load significantly increased (P ≤ 0.05). Finally, it was concluded that the improvement of water quality helps sustain the health of farmed fish .

Immunosaccharides such as β-glucans and fructooligosaccharide (FOS) strengthen the host’s immune responses. This study examined the influences of three levels of the β-1, 3 glucan-FOS combination on Red tilapia performance. Four diets were prepared: T₀ as a control, while T_0.5, T₁, and T_1.5 indicate the addition of β-1, 3 glucan-FOS mixture at 0.5%, 1%, and 1.5%, respectively. Then, 240 red Tilapia (Oreochromis niloticus x O. mossambicus) (weight 6.1 ± 0.07gm) were allocated into four groups, and every group was fed tested diets for 56 days. After the feeding trial, growth parameters, erythrogram profile, liver and kidney function testes, glucose, histopathological analysis, and gene expressions for antioxidants, catalase (CAT) and glutathione peroxidase (GPX) besides growth hormone (GH) and insulin-like growth factor 1 IGF1-related markers were assessed. Red tilapia fed T_0.5, T₁, and T_1.5 exhibited consistent growth, survival rate, and homeostasis compared with the control group. Different supplement concentrations displayed varying levels of responses. The hepatorenal biomarkers (alanine transaminase (ALT = SGPT) and aspartate transaminase (AST = SGOT), alkaline phosphatase (ALP = ALK), urea, and creatinine) and glucose showed a significant reduction in the supplemented groups compared with the control, especially in the T₁ and T_1.5 groups. The intestinal morphometric study revealed that fish group fed on T₁ represented the best result, whereas group T_1.5, followed by group T_0.5, was moderately treated, compared to the control. The real-time quantitative reverse transcription PCR (qRT-PCR) analysis displayed up-regulated expression of antioxidant and growth-correlated genes in the T_1.5 groups. After 56 days, the β-1,3 glucan-FOS fed groups also exhibited an increase in survival rates compared to the control when challenged with a pathogenic Vibrio alginolyticus. Current findings suggest that inclusion of β-1,3 glucan-FOS in diets could enhance red tilapia biochemical parameters, growth, and protection against pathogenic V. alginolyticus infection.