The Escalating threat of climate change-driven diseases in fish: Evidence from a global perspective - A literature review

A "proto" type galectin expressed in striped bass (Morone saxatilis) tissues is released to epidermal mucus and binds to bacterial and mucus glycans

Like all aquatic vertebrates and invertebrates, teleost fish are subject to the constant pressure of bacterial, fungal, and parasitic organisms present in the environmental interface that can potentially cause disease. Numerous defense molecules, including galectins, have been isolated from the skin and gut tissues of several marine and freshwater fish species. To provide new insights into the potential role(s) of galectins in the teleost fish innate immune system, we carried out studies on the striped bass (Morone saxatilis), a keystone fish species in Chesapeake Bay. We purified from epidermal skin mucus, and skin and muscle tissue, a 15-kDa galectin that we designated Msgal1-L1 (M. saxatilis galectin1-like protein 1). Both the transcript sequence and gene organization of Msgal1-L1 suggested a close relationship to the zebrafish galectin Drgal1-L2 and other proto type galectins from vertebrates, including the mammalian galectin-1. Glycan microarray analysis of Msgal1-L1 revealed a binding preference for Galβ1,4GlcNAc, and a homology structural model identified the amino acids involved in ligand recognition, both observations consistent with proto type galectins. Immunohistological examination localized Msgal1-L1 to epithelial and macrophage-/fibroblast-like cells in mucosal tissues, including skin and gill. The preliminary localization of Msgal1-L1 in free macrophage-like cells in epidermal mucus was corroborated by immunofluorescence analysis of macrophages isolated from head kidney. Msgal1-L1 binds in a carbohydrate-specific manner to O-glycosylated components of epidermal mucus. Msgal1-L1 agglutinated environmental bacterial species and strains, some of which are recognized fish pathogens, such as Vibrio and Edwardsiella spp. A microbial microarray analysis revealed that it preferentially binds to bacterial exopolysaccharides (e.g., Streptococcus and Shigella spp.) as well as various lipopolysaccharide O-antigen serotypes of Proteus spp. A preliminary solid-phase assay showed that Msgal1-L1 strongly bound Streptococcus sp., but very weakly to Mycobacterium marinum, an endemic pathogen of striped bass in Chesapeake Bay. Taken together, this evidence suggests that Msgal1-L1 may function in defense recognition against environmental bacteria by agglutinating and/or cross-linking them to mucus oligosaccharides to immobilize them within the epidermal mucus film and prevent their access to the fish epithelial cell surface. M. marinum would evade this defense mechanism to reach and infect the fish skin epithelial layer.

Seasonal and environmental drivers of antibiotic resistance and virulence in Escherichia coli from aquaculture and their public health implications

Aquaculture is increasingly impacted by environmental stressors such as temperature and pH fluctuations, which influence the proliferation and antibiotic resistance of Escherichia coli (E. coli). This study investigates the effects of these factors on the prevalence, virulence, and antibiotic resistance of E. coli isolated from aquaculture environments in Egypt, with a focus on public health implications. A total of 328 Oreochromis niloticus (Nile tilapia) samples were collected from Egyptian fish farms over five sampling periods, representing different seasonal conditions. E. coli was isolated and identified using selective culture methods and biochemical tests. Molecular characterization was conducted via polymerase chain reaction (PCR) to detect diarrheagenic E. coli pathotypes (st, lt, eaeA, bfpA, stx1, stx2). Additionally, PCR was utilized to screen for β-lactamase and carbapenemase resistance genes. Water parameters, including temperature and pH, were recorded, and their correlation with bacterial prevalence, virulence, and antibiotic resistance profiles were analyzed. A high prevalence of E. coli (92.68%) was observed, with a significant correlation between bacterial occurrence and elevated water temperatures. Diarrheagenic E. coli was detected in 82.1% of samples, with enterotoxigenic E. coli (ETEC) being the most common pathotype. Some isolates harbored multiple virulence genes, indicating hybrid strains. Resistance genes such as blaTEM, blaCTX-M, and blaOXA-48 were widely distributed, particularly during warmer months and at neutral pH levels. Groups with elevated water temperatures exhibited a higher prevalence of antibiotic-resistant isolates, often harboring multiple resistance genes. This study highlights the significant role of environmental stressors in influencing the prevalence, pathogenicity, and antibiotic resistance profiles of E. coli in aquaculture systems. The findings emphasize the need for continuous monitoring and improved biosecurity measures to mitigate the risks associated with MDR E. coli in aquaculture, ensuring food safety and protecting public health.

Weak monsoon signals detected in growth chronologies of lake fish on the Qinghai-Tibetan Plateau

Understanding the variation in fish growth responses to climate change across regions is essential for predicting fish population dynamics and relevant ecological consequences on a large scale. Despite the demonstrated sensitivity of fish growth responses to climate change on the Qinghai-Tibetan Plateau (QTP), the geographical variations in these responses remain unclear. This study analyzed the growth responses of schizothoracine fish to environmental variables in four geographically distinct QTP lakes (Qinghai Lake, Yamdrok Lake, Pangong Tso, and Co Nag) using otolith biochronologies and hierarchical mixed-effects modeling and quantified the relative contributions of intrinsic and extrinsic factors to fish growth variations. Overall, we found that the optimal model accounted for 82% of the annual growth variability. Age variables were the intrinsic factors primarily influencing fish growth (significant and negative, accounting for 92% of the explained variability), followed by the influence of extrinsic environmental factors at the local (i.e., air temperature and precipitation, significant and positive, 5%), global (i.e., sea surface temperature [SST], significant and negative, 2%), and regional (i.e., monsoon intensity, nonsignificant and negative, 0.4%) scales. At the lake level, the influences of environmental factors on fish growth aligned with overall results but showed varied contributions. Therefore, local factors primarily influence fish growth responses, emphasizing that geographical variations in fish responses to climate change should be accounted for in relevant population predictions. This study provides valuable insights into the complex interactions between fish growth and multi-scale environmental changes and offers scientific support for ecosystem management under climate change on the QTP.

Dose response effects of dietary clove and peppermint oils on the growth performance, physio-metabolic response, feed utilization, immunity, and organ histology in African catfish (clarias gariepinus)

Phytochemicals and essential oils have been widely used as growth promoters in aquaculture. However, the optimal dose of a blend of essential oils for promoting the growth and health of African catfish (Clarias gariepinus) remains largely unknown. Therefore, the present study aimed to assess the dose-response effects of dietary supplementation with a blend of clove and peppermint oils (CPO) on growth indices, feed utilization, physio-metabolic responses, immunity, and organ histology in African catfish. Catfish (105.1 ± 0.5 g) were fed diets containing 0.0 (control; CPO0), 1.0 (CPO1), 2.0 (CPO2), or 3.0 mL CPO/kg diet for two months. The results displayed that fish performance and feed intake significantly improved with increasing CPO levels in a linear manner (P < 0.01). Additionally, the specific growth rate and hemoglobin (R2 = 84.6%) levels showed quadratic improvements with the optimal doses at 1.12 mL and 1.6 mL/kg diet, respectively. The inclusion of dietary CPO linearly affected aspartate aminotransferase (AST; R2 = 93.1%), alanine aminotransferase (ALT; R2 = 97.7%), alkaline phosphatase (ALP; R2 = 97.0%), and glucose (R2 = 85.9%) levels in the plasma of catfish (P < 0.001). Increasing the concentrations of dietary CPO led to a quadratic decrease in creatinine (R2 = 98.7%), uric acid (R2 = 94.8%), and cortisol (R2 = 87.1%; P < 0.001), with optimal doses confirmed at 1.75, 2.7, and 1.3-mL CPO per kg of diet, respectively. Dietary CPO has a significant modulatory impact on immune-antioxidant variables in African catfish in a dose-dependent manner. Increasing CPO in the fish diets resulted in a quadratic increase in the levels of immunoglobulin G (IgG; R2 = 98.8%), lysozyme activity (R2 = 93.9%), and total antioxidant capacity (R2 = 84.9%). The corresponding dose-response curves displayed that the optimal doses were at 1.85, 2.1, and 1.8 mL/kg of diet. Furthermore, superoxide dismutase (SOD), and reduced glutathione (GSH) levels were significantly improved in all CPO-treated groups in a quadratic manner, with optimal doses at 1.25 mL (R2 = 90.6%) and 1.55 mL (R2 = 89.7%) per kg of diet. Catfish fed diets supplemented with CPO showed gradual improvements in hepatocytes (HP), and blood vessels (BV) with an increased number of binucleated cells. Moreover, catfish fed diets containing CPO had improvement in the tubular epithelium, Bowman's capsule, and a few melanomacrophage areas. This study revealed that CPO supplementation at an optimal dose of 1-2 mL/kg of diet significantly improved growth performance, feed utilization, metabolic processes, and immune and antioxidant functions in African catfish.

Effects of nano-selenium and/or vitamin E supplementation on growth performance, antioxidant status, histopathology and resistance to Aspergillus flavus in Nile tilapia (Oreochromis niloticus)

BACKGROUND

This study aimed to evaluate the effects of selenium nanoparticles (SeNPs) and/or vitamin E (VE) on the growth, body composition, metabolic parameters, histopathology, and resistance of Nile tilapia to Aspergillus flavus.

RESULTS

Monosex Nile tilapia fingerlings were sourced from the Bazina farm and hatchery in Ismailia Governorate, Egypt, where the experiment was also conducted. The fish were acclimatized for 15 days before the trial. A total of 240 fingerlings (average weight 46 ± 3.0 g/fish) were divided equally across 12 concrete tanks (1 × 1 × 1.2 m, 1 m³ capacity), with 20 fish per tank. The fish were fed a control diet (T0), which was a basal diet with no supplementation, or one of three experimental diets for 60 days: T1 (1 mg SeNPs/kg), T2 (100 mg VE/kg), and T3 (1 mg SeNPs + 100 mg VE/kg). The experiment followed a completely randomized design (CRD) with three replicates per treatment. The combination of SeNPs and VE (T3) resulted in the best feed conversion ratio. A slight but significant increase (P < 0.05) in whole-body composition was observed in all treatment groups compared to the control. Biochemical parameters, serum digestive enzyme activity, and antioxidant levels improved significantly with dietary supplementation. Histopathological analysis revealed somewhat lacerated gill arches in fish fed SeNPs, VE, or their combination, but the overall gill structure remained normal. The SeNPs + VE group exhibited improved villi length and normal morphology of portal veins and hepatic sinusoids, though some vacuolated hepatocytes were noted. Fish in the SeNPs + VE group had the lowest mortality rates and the highest resistance to A. flavus.

CONCLUSION

Supplementing diets with SeNPs and/or VE enhances growth, body composition, biochemical parameters, and histopathology in Nile tilapia. The combination of 1 mg SeNPs + 100 mg VE/kg improves immune response and growth, offering a promising strategy to enhance Tilapia health and productivity.