Journal of fish diseases最新文献

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.

Fish susceptibility to parasitic infection is a crucial issue in aquaculture, where the density of captive fish increases the intensity of parasitic infections. Monogeneans are a group of parasitic flatworms that include pathogenic species for fish, among them Neobenedenia spp., which pose significant challenges for fish health in farming systems. Understanding the dynamics of parasitism in fish and how they may vary according to host susceptibility or environmental conditions is essential for the development of effective management strategies in aquaculture. Therefore, the aim of this study was to investigate the individual susceptibility of Almaco jack (Seriola rivoliana) to infections by Neobenedenia sp. and examine how reinfection affects parasite load in an aquaculture setting. Our findings unveiled an aggregated distribution of parasites in the fish population, indicating a non-random pattern influenced by specific host factors. Furthermore, our results revealed that even minor temperature variations, such as an increase of just 1°C, were associated with a noticeable rise in parasite abundance. These results underscore the importance of regular monitoring in S. rivoliana tank-maintained systems, as even minor temperature fluctuations can cause a substantial increase in Neobenedenia sp. infections, particularly in more susceptible individuals.

MicroRNA-33 (miR-33) plays a critical role in the regulation of autophagy and inflammatory responses. In this study, C. idella kidney (CIK) cells were transfected with a miR-33 mimic or inhibitor and Atg5 was overexpressed or silenced to elucidate the regulatory mechanism of miR-33. Our findings revealed that the miR-33 mimic significantly decreased the expression of LC3B (a marker of autophagy activation), and the level of autophagy-related genes (Beclin-1, Atg5 and LC3-1) was also significantly downregulated (p < 0.05). Additionally, the miR-33 mimic promoted the secretion of proinflammatory factors, including TNF-α, IL-6, IL-12 and IL-1β (p < 0.05). In contrast, the miR-33 inhibitor significantly enhanced LC3B protein expression and increased the relative expression of Beclin-1 and Atg5 (p < 0.05). The secretion of proinflammatory factors (TNF-α, IL-6 and IL-12) was significantly reduced (p < 0.05). These results suggested that inhibition of miR-33 could induce the initiation of autophagy and attenuate the inflammatory response in CIK cells. Furthermore, we identified Atg5 as a direct target gene of miR-33. Overexpression of Atg5 significantly upregulated the levels of Beclin-1, Atg5, Atg4C and LC3-1, along with a reduction in the secretion of proinflammatory factors (TNF-α, IL-12 and IL-1β). Besides, the activities of superoxide dismutase (SOD) and catalase (CAT) were significantly increased (p < 0.05). Conversely, interference with Atg5 expression caused significant downregulation in the expression levels of Beclin-1, Atg5, Atg12, Atg4C and LC3-1, resulting in increased secretion of TNF-α, IL-12 and IL-1β and decreased activity of acid phosphatase (ACP) and SOD (p < 0.05). Taken together, these results suggested that inhibition of miR-33 expression could promote the initiation of autophagy and attenuate the inflammation in CIK cells through targeting Atg5. This study not only enhances the understanding of the mechanism by which miR-33 regulates autophagy and inflammation in fish but also provides a theoretical foundation and novel insights to improve disease management in the fish aquaculture industry.

Lumpfish are commonly used as cleaner fish in the production of Atlantic salmon as a preventive measure against sea lice. This, and other procedures, are stressful and may harm the cleaner fish. In this work, lumpfish skin was studied to understand this organ better and to develop tools to analyse and monitor lumpfish skin health. Three different sample sets were used: preadult lumpfish from a land-based hatchery, adult lumpfish from a salmon farm and adult lumpfish before and after a delousing at a commercial salmon farm. We developed a digital histomorphometric algorithm in Aiforia to better quantify structures and measure skin features and to study the effects of delousing treatment on lumpfish skin. Results show that lumpfish skin is highly complex. The specific cells and their integrity are important for the fish to maintain homeostasis and protect against the outer environment. Damages in skin are induced during or after delousing, and these damages may make the fish more susceptible to secondary infections. The detected damages may be difficult to observe through visual inspections, and in-depth analyses at the cellular level may be needed to understand the impact of different stressors on lumpfish health.

Lymphocystis disease virus (LCDV) infection induces massive hypertrophy of dermal cells with intracellular accumulation of virions, resulting in skin nodules that are observed to the naked eye. In September 2022, an ornamental fish producer noted white spots and nodules on the skin and fins of a three-spot gourami (Trichogaster trichopterus) population, which compromised the aesthetic of the fish. The disease only affected this fish species in the farm and was intermittent. Ten diseased and four apparently healthy fish were collected during the first sampling, and 20 diseased fish were collected approximately 1 year after for a follow-up examination. Macroscopically, the fish presented isolated or small clusters of white to grey nodules, measuring 0.1-0.5 mm, concentrated on the fins and caudal peduncle. Histologically, nodules in the skin and internal viscera were composed of numerous hypertrophied cells with nucleolar components and karyomegaly and thick hyaline cell walls. Virions, with a diameter of approximately 180 nm, were visualised in infected interstitial cells in the skin through transmission electron microscopy. The presence of LCDV in the skin, spleen, and kidney was confirmed by specific PCR. Phylogenetic analysis of the MCP gene revealed that the isolates from Brazilian gouramis belonged to the cluster of LCDV genogroup VI, similar to an unclassified virus identified in a population of gouramis in Korea. This report describes the pathological and molecular findings of LCDV infection in cultured three-spot gourami in Brazil.

This is a case study that assessed risk factors for transmission of red sea bream iridovirus (RSIV) focused on cross-contamination of aquaculture equipment in semi-open system aquaculture. Our investigation during the RSIV outbreak in the fish farm demonstrated that equipment used for collecting dead fish, such as landing nets and gloves, was highly contaminated with RSIV. Based on the results, a daily operation for collecting dead fish was implemented, starting with net pens where no disease occurred, followed by the net pen where the RSIV outbreak occurred to prevent fomite transmission via RSIV-contaminated equipment. In addition, the landing nets used for collecting dead fish were disinfected at the end of each day to avoid carryover of the virus to the following day. RSIV was not transmitted to the other net pens in the fish farm for more than 30 days. However, once an RSIV outbreak occurred in the net pen that was upstream in the operation for collecting dead fish, RSIV was transmitted to all net pens in approximately 1 week, implying that the transmission was caused by cross-contamination. This study suggested that appropriate hygiene management is important to prevent fomite transmission between net pens, even in semi-open system aquaculture.