Journal of fish diseases最新文献

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.

Salovirus is a genus within the family Caliciviridae, which contains a single member species, Salovirus nordlandense, also known as Atlantic salmon calicivirus (ASCV). While previous work has shown that ASCV can replicate in fish cell lines and establish systemic infection in vivo, its exact role in disease remains unclear and very little is known about its geographic distribution and evolution among Atlantic salmon. To expand the phylogenetic range of ASCV and better understand its potential role in disease, we screened publicly available transcriptomes for ASCV-like sequences. Notably, we detected ASCV in sequencing projects of Atlantic salmon (Salmo salar) (n = 40) and wild common whitefish (Coregonus lavaretus) (n = 1), across Chile, Scotland and Norway. Our phylogenetic analysis identified two viral species, which we provisionally name Salovirus nordlandense 1 and 2, each containing distinct genotypes. Both viral species were found in all three countries, with no clear geographic pattern, indicating that saloviruses have spread through the Atlantic salmon trade. It was notable that 88% of these transcriptomes were generated for the study of other pathogens, including infectious salmon anaemia virus, piscine myocarditis virus and Piscirickettsia salmonis, suggesting that saloviruses might be frequently associated with co-infections. Overall, this study indicates that viruses, like ASCV, can silently spread through aquacultural practices, potentially contributing to a variety of fish diseases.

Nocardia seriolae is the main pathogen causing fish nocardiosis, which can infect various aquatic freshwater and marine fish species. We have previously confirmed that the heme-binding protein of N. seriolae (NsHBP) is a secreted protein relating to bacterial virulence. In the present study, a ΔNsHBP mutant of N. seriolae was successfully generated by deleting NsHBP gene, and it was further used for attenuated vaccine development and evaluation in hybrid snakehead (Channa maculata ♀ × Channa argus ♂). The LD₅₀ of strain ΔNsHBP by intraperitoneal injection in hybrid snakehead was presented at 5.47 × 10⁷ CFU/mL, significantly (p < 0.01) higher than that of the wild-type strain at 5.28 × 10⁵ CFU/mL, indicating the virulent reduction of strain ΔNsHBP in comparison to wild-type strain. The live attenuated vaccine used strain ΔNsHBP at sub-clinical dosages (LD₁₅, 1.26 × 10⁷ CFU/mL) to immunise the fish by intraperitoneal injection for 56 days could provide a relative percentage survival (RPS) at 82.40% against artificial challenge with wild-type strain ZJ0503. Additionally, serum enzymes activities of lysozyme (LZM), peroxidase (POD), acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase (SOD) as well as specific antibody (IgM) titers were induced in fish following ΔNsHBP vaccination. Furthermore, the expression of immune-related genes (TNFα, IL-1β, MHCIα, MHCIIα, CD4 and CD8α) was significantly increased in comparison to the control group during immunisation period with ΔNsHBP in fish. Taken together, it is revealed that the deleted strain ΔNsHBP could be a potential candidate for live attenuated vaccine development to control fish nocardiosis in aquaculture.

Effective sample preservation is essential in large-scale population monitoring, particularly for molecular genetic analyses of pathogens, and for measuring disease symptoms in hosts. In such monitoring cases, disease symptoms can indicate poor habitat health, as they often coincide with elevated temperatures and suboptimal environmental conditions. This study examines the effect of two preservatives; 95% ethanol and 99% isopropanol on the assessment of proliferative kidney disease (PKD) in the renal tissue of young-of-the-year brown trout (Salmo trutta). Specifically, we studied the effect of preservatives on the physical measurement of a primary symptom of PKD, renal hyperplasia. Furthermore, we evaluated the effect of preservatives on the molecular detection and quantification of the causative PKD agent myxozoan parasite Tetracapsuloides bryosalmonae. Our results indicate that isopropanol-preserved samples exhibit greater renal tissue shrinkage, with the most pronounced differences observed in smaller fish when compared to ethanol-preserved samples. This difference in shrinkage is great enough to disguise symptomatic fish when observing renal hyperplasia with mixed storage mediums. However, both preservatives were found to be suitable for DNA extraction of sufficient quality for detection and quantification of the parasite using qPCR with no statistically significant differences in DNA yield or parasite load due to the type of preservative. We found that while ethanol is preferable for ease of dissection, isopropanol is a suitable alternative for PKD monitoring in wild fish, especially where access to ethanol may be limited. Understanding the difference in tissue shrinkage caused by the two preservatives can enable compensatory adjustment and maintain higher standards of data accuracy when assessing the severity of Tetracapsuloides bryosalmonae infection.

The Ameson portunus is a prevalent pathogen affecting Portunus trituberculatus, which can infect P. trituberculatus and cause albinism, seriously damaging its economic value. Therefore, there is a pressing need for an efficient detection platform to rapidly and sensitively identify A. portunus. In this study, we have developed a method known as recombinase polymerase amplification combined with lateral flow dipstick (RPA-LFD) for the swift detection of A. portunus. Three sets of specific primer pairs and a probe were designed according to the spore wall protein (SWP) sequence of A. portunus, in which one of the primer pair (ApSWP-F1/R1) showed the best amplification effects. The optimal reaction temperature was ultimately determined to be 39°C and the optimal reaction time was set at 10 min after careful optimisation of both variables. The sensitivity of the RPA-LFD method was better than that of polymerase chain reaction (PCR), with a limit of 1.71 × 10^-4 ng/μL. This RPA-LFD detection method has good specificity for the detection of A. portunus, and tests for other parasites such as Zschokkella ophiocephali, Myxobolus drjagini, Myxidium lieberkuhni and Pelteobagrus fulvidraeo are negative. The above results show that the RPA-LFD detection method of A. portunus established in this study has strong specificity, high sensitivity, simple operation and visual results, which can be widely used for rapid detection on site.