Journal of fish diseases最新文献

Rahnella aquatilis as an emerging pathogen can cause bacterial enteritis in cyprinid fish such as crucian carp Carassius auratus. Currently, the characterisation of immune function and gut microbiome composition in C. auratus orally challenged by R. aquatilis were yet unknown. In this study, we therefore investigated the changes of histopathology, white blood cells (i.e., LEU, NEU and LYM), serum biochemical indicators (e.g., CRE, CK and CHO) and digestive enzyme activity (e.g., LYS, AST, ALT, GSH-Px and AKP), as well as complements and immune-related genes (e.g., C3, F2, LysC, TLR3, MyD88, TGF-β, TNF-α and IL-15) that were significantly altered after the oral administration of R. aquatilis KCL-5. Moreover, the gut microbiome composition and diversity were analysed by using 16S rRNA gene high-throughput sequencing analysis. The correlation analysis showed that the high abundance of phylum Proteobacteria, Actinobacteria, Firmicutes and Fusobacteria was related to the pathogenesis of enteritis caused by oral infection. KEGG enrichment analysis indicated that fatty acid, carbon and pyruvate metabolism were significantly increased pathways (p < 0.05). To our best knowledge, this is a rare report of physicochemical properties and gut microbiome in C. auratus by R. aquatilis infection, which will provide a scientific reference for the clinical diagnosis and prevention of bacterial enteritis in cyprinid fish.

In Chile, Atlantic salmon and rainbow trout face significant production challenges due to the presence of Flavobacterium psychrophilum, which generates severe disease issues and economic losses. To address this, the salmon industry relies on vaccines and antibiotics, the latter raising concerns about bacterial resistance. For that reason, our study explores an alternative strategy for controlling F. psychrophilum infections based on host defence peptides. We previously identified and characterised IL-8-derived salmonid peptides (ssIL-8α and omIL-8α) with potential antimicrobial properties. In the current study, we further investigated the antibacterial activity and mechanism of action of these peptides against F. psychrophilum. First, we demonstrated the antibacterial activity of ssIL-8α and omIL-8α synthetic peptides. Then we evaluated the effects of these peptides on membrane fluidity and localisation on bacterial cells by fluorescence microscopy as well as its impact on bacterial morphology and ultrastructure by electron microscopy. The results indicate that the ssIL-8α at 30 μM exhibits superior efficacy in inhibiting the growth of F. psychrophilum. Also, both ssIL-8α and omIL-8α can bind to pathogen membrane, but ssIL-8α exhibits a higher binding capacity compared to omIL-8α against F. psychrophilum. omIL-8α exhibited the ability to induce early membrane alterations within 15 min, at concentrations of 15 or 30 μM. The SEM and TEM micrographs showed membrane disruption of the bacteria after incubation with ssIL-8α or omIL-8α. However, the damage was more pronounced in the ssIL-8α treatment, as evidenced by a complete detachment of the outer membrane after a 20-min exposure of F. psychrophilum. This study reveals that these peptides significantly alter bacterial membrane morphology, leading to bacterial death, highlighting their potential as alternative treatments in flavobacterial disease control. This work contributes to understanding host defence peptides' role in combating bacterial infections and reducing antibiotic resistance in aquaculture.

Myxobolus Bütschli, 1882 is a highly important genus of fish myxozoans, consisting of many species that cause serious diseases in ornamental cyprinid fish species in different geographic areas by infecting a wide range of organs. This study describes a new Myxobolus species infecting the gill lamellae, gill rakers and skin epidermis of goldfish (Carassius auratus) from Mohammadshahr, Iran, based on detailed morphological, histological and molecular analysis. Mature spores were small and spherical in shape, consisting of two symmetrical shell valves in frontal view, measuring 10.3 (9.8-10.9) μm in length and 10.5 (10.3-11.2) μm in width. Two equal-sized relatively pyriform polar capsules were 5.4 (3.9-6.0) μm long and 4.5 (3.7-5.2) μm wide. The polar tubules were coiled with 4-6 turns. A comparative analysis of the morphological and molecular data confirmed that this species is distinct from other identified myxosporeans. Plasmodia in the cutaneous tissue were found in the epidermis, causing extensive hyperplasia of Malpighian cells and mild inflammatory infiltration. In the gill tissue, plasmodia affected only one side of the lamellae, leading to hyperplasia of the lamellar epithelium, edema, and lymphoplasmacytic branchitis. A novel myxozoan species, Myxobolus branchioepidermis n. sp., has been proposed. The study provides a comprehensive analysis of the morphological, histological, and molecular characteristics of this parasite, which infects the gill lamellae and epidermal layer of the skin in oranda goldfish (C. auratus). The identification of this new species adds to the growing body of research on myxozoan parasites and highlights its potential impact on ornamental fish aquaculture.

Infectious spleen and kidney necrosis virus (ISKNV) and nervous necrosis virus (NNV) are two common and important causative agents in marine-cultured fish. However, high viral loads of both ISKNV and NNV in the same clinical case is unusual. In this study, a mass mortality event of Asian seabass Lates calcarifer juveniles occurred in Zhuhai, the main Asian seabass cultured area in mainland China. The fish samples were pooled for pathogen identification and both high viral loads of ISKNV and NNV were detected by real-time microfluidic quantitative PCR and conventional PCR. Immunohistochemistry and immunofluorescence showed that strong ISKNV signals were detected in spleen and liver, while strong NNV signals were detected in brain and eye. The tissue homogenates were inoculated into MFF-1 cell and SSN-1 cell, respectively. After several viral passages, both individual ISKNV and NNV were purely isolated from each other, and designated as ASB-ISKNV-23 and ASB-NNV-23, respectively. The whole genome sequences of ASB-ISKNV-23 and ASB-NNV-23 were determined and annotated. The result showed that ASB-ISKNV-23 and ASB-NNV-23 are composed of 112,236 bp and 4441 bp, respectively. Phylogeny analysis showed that ASB-ISKNV-23 belongs to ISKNV-II sub-genotype and ASB-NNV-23 belongs to RGNNV genotype. Collectedly, coinfection of ISKNV-II and RGNNV were firstly documented in mass mortality of Asian seabass in mainland China. Importantly, both individual ISKNV-II and RGNNV were purely isolated using two different permissive cell lines. Our study provides useful information for better understanding the complex pathogenesis regarding the coinfection with ISKNV and NNV in farmed fish.