Journal of fish diseases最新文献

Lactococcosis, primarily caused by Lactococcus garvieae, is prevalent in various freshwater fish species globally. Yet, its significance in Thai fish aquaculture remains poorly understood. This study investigated Lactococcosis-associated diseases across four red tilapia (Oreochromis sp.) and one Asian sea bass (Lates calcarifer) farm in Thailand in 2022. Chronically diseased fish displaying clinical signs such as exophthalmia or corneal opacity, erratic swimming, scale loss and skin haemorrhage, as well as apparently healthy specimens, were studied. Bacterial isolation was performed from the fish internal organs. Gram-positive bacterial isolates were selected and later identified as L. lactis (n = 4), L. taiwanensis (n = 1), L. garvieae (n = 2) and L. petauri (n = 2) based on bacterial 16S rDNA and gyrB partial sequences. Sub-adults of Nile tilapia were intracoelomic (IC) injected with representatives of each of the three Lactococcus species (L. garvieae, L. lactis and L. taiwanensis) at varying doses (10³-10⁷ CFU/fish), while juvenile Asian sea bass were IC injected with L. petauri at doses ranging from 10² to 10⁸ CFU/fish. Control groups received culture medium alone. By the end of the 21-day test, mortality rates from all challenge groups ranged from 0% to 14.82%. Some clinical signs were observed in groups challenged with higher doses of the bacteria. Enzyme-linked immunosorbent assay (ELISA) showed that survivor fish exposed to high bacterial doses elicited specific antibodies IgM. In summary, this study identifies the presence of Lactococcus species in farmed fishes, which exhibit low virulence in Nile tilapia and Asian sea bass under laboratory-controlled challenges. These bacterial isolates appear to be opportunistic rather than pathogenic, potentially indicating underlying health challenges within the affected farms.

Hybrid yellow catfish (Tachysurus fulvidraco♀ × Tachysurus vachelli♂) is a significant aquaculture variety in China. It is easy to be infected by trichodinids, causing serious economic losses. However, the species investigation of trichodinids on hybrid yellow catfish is relatively deficient, which seriously hinders the prevention and control of trichodiniasis. Hence, trichodinids were collected in a hybrid yellow catfish farm in Hubei Province from June 2022 to October 2023 and identified by morphological and molecular biology methods. A new species Tripartiella luhuensis sp. nov. and nine Trichodina species were described. Phylogenetic analyses demonstrated that T. luhuensis nested in the Trichodinella-Tripartiella-Paratrichodina clade, indicating that the genus Tripartiella is not a monophyletic group. Besides, Trichodinid species from Siluriformes hosts have relatively similar evolutionary positions. Histopathological analysis revealed that the parasitism of trichodinids caused mechanical damage and mucus hypersecretion to gill of the host. The present study reports trichodinid species on hybrid yellow catfish for the first time and adds one new species to the genus Tripartiella. We also indicate the importance of preventing and controlling trichodiniasis in hybrid yellow catfish farming.

Piscine francisellosis is a highly infectious and economically significant disease caused by Francisella orientalis in tilapia (Oreochromis spp.). There are currently no approved treatments or commercial vaccines for this disease in cultured fish. Injectable vaccines using diatoms as antigen expression vectors have demonstrated efficacy in tilapia models; however, no oral vaccine trials have been performed. We hypothesised that fusion proteins consisting of F. orientalis IglC and flagellin expressed in Thalassiosira pseudonana diatoms will act as self-adjuvanting antigen delivery systems to confer a protective immune response against F. orientalis in tilapia when administered as top-coated feed. Different treatments were immunised and subsequently provided with one or two boosters prior to challenge. Fish were challenged with virulent F. orientalis via immersion thirty days post initial immunisation. Tilapia immune response was assessed 24 h post-challenge by quantifying il-12, il-10, ifn-γ and tgf-β gene expression in gills and internal organs. Morbidity and mortality were monitored for 21 days after challenge and bacterial load was assessed in survivors. Findings indicate significant changes in the expression of ifn-γ and tgf-β in immunised fish, but similar mortality rates and bacterial load across all exposed groups.

Tilapia lake virus disease (TiLVD), which is caused by tilapia lake virus (TiLV), has resulted in significant damage to global tilapia farming. TiLV is a negative-sense single-strand RNA virus consisting of 10 genome segments. To date, no commercial vaccine against TiLVD has been developed, and effective strategies to control and prevent TiLVD are lacking. In this study, we developed and tested a chitosan nanoparticle-based immersion recombinant protein targeting segment 4 (S4) of TiLV under both laboratory and field conditions. The open reading frame of S4 of TiLV was cloned into pET28a (+) and expressed by Escherichia coli BL21(DE3). The size of the nanoTiLV-S4 (CNS4) vaccine was 284 ± 9.2 nm, which is smaller than the pre-nanoencapsulation vaccine size of 2268 ± 41.8 nm. Transmission electron microscopy revealed that the nanoS4 particles had a round shape, uniform appearance and positive zeta potential of 17.7 ± 0.7 mV. Further analysis showed that the nanoS4 antigen was deposited on the fish gills and intestines and taken up into the epithelial cells within 30 min of immersion. Under laboratory infection using a cohabitation challenge model, the CNS4 vaccine demonstrated a relative percent survival (RPS) of 25%. In field conditions, the vaccine showed an RPS of 31.88% compared to the unvaccinated group. Overall, our study demonstrates that the new nanoTiLV-S4 vaccine can be absorbed by the fish epithelium and reduces mortality caused by TiLV. However, further optimisation and field trials are necessary to improve the efficacy of the CNS4 vaccine and to test it under various farm conditions.

Infectious spleen and kidney necrosis virus (ISKNV) has a broad host range and poses a significant threat to aquaculture species. Herein, we report two disease outbreaks in snakeskin gourami (Trichopodus pectoralis) in Thailand, marked by skin haemorrhage, scale loss, internal organ discoloration and degeneration and a mortality exceeding 60%. Additionally, three spot gourami (Trichopodus trichopterus) cultured in the same ponds along with snakeskin gourami were found to be affected and tested positive for the virus. Histopathological examination revealed extensive necrosis of haematopoietic tissues in the kidneys and spleen, accompanied by the presence of numerous megalocytic cells in both fish species. Real-time PCR assays, using protocols targeting the major capsid protein (MCP) gene in a broad range of Megalocytivirus genotypes, confirmed the presence of ISKNV in the infected fish. Furthermore, molecular and phylogenetic analyses based on the MCP gene (1362 bp) and the adenosine triphosphatase (ATPase) gene (720 bp) revealed that the ISKNV strains in gourami and other fish hosts were closely related, suggesting possible cross-species transmission. This report extends the host range of ISKNV and highlights the need to prevent the spread of this virus across species boundaries. Further research is needed to understand the pathogenicity and transmission routes of the virus, gain insights into its epidemiology and develop strategies to mitigate disease outbreaks.

The bacterial skin disease tenacibaculosis, caused by Tenacibaculum species, affects numerous economically important marine fish, including salmonids. This study reports the ability of three Tenacibaculum maritimum strains, belonging to different molecular O-AGC types, and a single Tenacibaculum dicentrarchi strain to induce tenacibaculosis in farmed Chinook salmon (Oncorhynchus tshawytscha, Walbaum 1792) in Aotearoa New Zealand. Naïve Chinook salmon were exposed to T. maritimum (2 × 10⁸ cells/mL) and T. dicentrarchi (2 × 10⁷ cells/mL) by immersion using natural seawater. Clinical signs of tenacibaculosis were apparent in all T. maritimum strains used in the challenged fish. Of these, 100% of the fish challenged with O-AGC Type 2-1 and Type 3-2 strains became moribund, whereas only 60% of the O-AGC Type 3-0 challenged fish became moribund. Fish exposed to T. dicentrarchi showed more severe symptoms, exposing musculature in 51% of the challenged population, with 28% of fish becoming moribund. Gross pathological signs of fin rot, scale loss, skin ulcers and haemorrhagic skin spots were observed for both Tenacibaculum species and were consistent with those observed on farmed fish. Pure T. maritimum and T. dicentrarchi cultures were reisolated from epidermal damage of challenged fish. Tenacibaculum species was not isolated from the anterior kidney of affected fish, which indicates no systemic infection in Chinook salmon.

Blood sampling of fish has received increasing interest from the industry. However, the impact of puncturing the caudal vasculature, a common sampling procedure, is poorly described. In this study, the histopathology of this procedure was examined in both acute and chronic stages.

Monogeneans are ectoparasitic flatworms causing significant economic losses in aquaculture. This study aimed to identify potential anthelmintic agents against these parasites by integrating computer-aided drug design (CADD) and in vivo evaluation. The β-tubulin gene, a well-established anthelmintic target, was cloned from Gyrodactylus kobayashii and its three-dimensional structure was generated using homology modelling. Virtual screening of 2319 FDA-approved drugs and nine common benzimidazoles against the modelled β-tubulin identified several promising compounds with low binding energy. Subsequent in vivo anthelmintic efficacy and acute toxicity assays in goldfish revealed etravirine as a potent candidate with an EC₅₀ value of 0.55 mg/L and a therapeutic index (TI) greater than 18.18. This favourable safety profile highlights etravirine's potential for controlling monogenean infections in aquaculture. Flubendazole and mebendazole also demonstrated potent anthelmintic activity, with EC₅₀ values of 0.022 and 0.023 mg/L and therapeutic indices exceeding 45.45 and 43.48, respectively. Molecular dynamics simulations confirmed stable binding modes for flubendazole and mebendazole with β-tubulin, providing mechanistic insights into their anthelmintic activity. Overall, this study demonstrated the utility of CADD in identifying potential therapeutic agents against monogenean and underscored the importance of β-tubulin as a key target for anthelmintic therapy, contributing to the development of sustainable aquaculture practices.

In August 2024, a significant fish kill involving hundreds of flathead grey mullet (Mugil cephalus) was reported in the delta region of the Karteros River, Crete, Greece. The investigation identified the primary cause of mortality as severe parasitic infections, specifically from the protozoan parasites Amyloodinium ocellatum and Trichodina sp., both of which heavily affected the gills of the fish. Concurrently, poor water quality in the area, likely due to reduced water volume and limited water renewal, created favourable conditions for parasite proliferation while weakening the fish's natural defences. This event raised concerns due to the location of the fish kill in the Karteros River delta, a highly protected area designated as a small island wetland.

Nile tilapia (Oreochromis niloticus) is an important food source worldwide and plays a significant role in Mexico's aquaculture industry. However, it faces increasing challenges from disease outbreaks threatening this sector. From recent research and epidemiological data, this review examines the diseases impacting tilapia aquaculture in Mexico. It analyses bacterial, parasitic, viral, and fungal infections, providing insights into their clinical signs, etiological agents, treatment strategies, and geographical distribution across various Mexican states. The study highlights four major parasitic infections: Cichlidogyrus Infection, Gyrodactyliasis, Neobenedeniosis and Trichodiniasis. Six prominent bacterial infections are discussed, including motile Aeromonas septicaemia (MAS), Streptococcosis, Staphylococcosis, Francisellosis, Edwardsiellosis and Mycobacteriosis. It addresses Saprolegniasis, a fungal infection affecting tilapia eggs and the overall health of hatcheries. Additionally, it highlights technical information on the Tilapia Lake Virus (TiLV), which poses a significant viral threat. This analysis examines the three-level diagnostic system for infectious diseases in aquaculture outlined by the FAO, emphasising its application in tilapia aquaculture in Mexico. The system includes (i) implementing prevention strategies, biosecurity protocols and good management practices (Level I); (ii) conducting laboratory-based diagnostic tests (Level II); and (iii) utilising advanced molecular techniques for early disease detection (Level III). By adopting these measures, the aquaculture sector can effectively mitigate disease outbreaks, thereby promoting the sustainable growth and long-term success of tilapia farming in Mexico.