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Salmon‐lice have the potential to change the behaviour and growth of their salmonid host species. Here, the baseline infection levels of salmon‐lice of post‐smolts (n = 815) and veteran migrants (n = 875) of sea‐run Arctic charr (Salvelinus alpinus Linnaeus, 1758) were monitored over two successive years in a sub‐Arctic Norwegian fjord without farming of salmonids. All Arctic charr were collected after the sea‐migration period from a trap placed in the river, ascending to their overwintering freshwater habitat (Lake Laksvatn). The sea‐lice infection showed a stable infection across the 2 years while increasing through the migration period and with the size of the wild sea‐run Arctic charr. The prevalence of sea‐lice infection was intermediate to high, and the intensities of sea‐lice infections observed were generally modest, although some individuals had high infections. The relatively high infection of salmon‐lice highlights the potential detrimental effects these parasites can have at both the individual and population level of such endangered sub‐Arctic life‐history strategies. A comparative study should be performed in fjords with aquaculture activity as focal points for salmon‐lice, to investigate the impact farming have on sea‐run Arctic charr populations. [ABSTRACT FROM AUTHOR]

The relatively unknown genus Iodobacter sp. has been repeatedly isolated from skin ulcers and saprolegniosis on freshwater fish in Finland, especially farmed salmonids. Genetic characterization verified that all 23 bacterial isolates studied here belonged to the species Iodobacter limnosediminis, previously undescribed from the fish microbiota. Whole‐genome pulsed‐field gel electrophoresis revealed variability between the I. limnosediminis strains, suggesting that they were most likely of environmental origin. Two I. limnosediminis strains caused lesions in 27%–53% of brown trout (Salmo trutta) injected intramuscularly (p ≤.05). The lesions represented moderate to severe tissue damage, but for most fish, the tissues had been repaired by the end of the experiment through the accumulation of fibrocytes and macrophages at the site of the lesion. I. limnosediminis was reisolated from some lesions and/or internal organs. Phenotypically and biochemically, I. limnosediminis resembles several common bacterial species found in the aquatic environment, as it grows well on several media as whitish medium‐sized colonies, is Gram negative and rod‐shaped. Here, we characterized I. limnosediminis strains with several methods, including MALDI‐TOF. This characterization will help in further investigations into the occurrence and possible involvement of I. limnosediminis in skin lesions of freshwater fish. [ABSTRACT FROM AUTHOR]

Keywords: Central Europe; Discocotylesagittata; Monogenea; trout EN Central Europe Discocotylesagittata Monogenea trout 1643 1646 4 09/16/21 20211001 NES 211001 The Museum Niederösterreich, Haus für Natur (St. Pölten, Lower Austria), features a large fish exhibition. However, the fact that the parasite was most likely introduced to the aquarium with rainbow trout or brown trout from a German or Austrian aquaculture farm certainly deserves attention. The population dynamics of the monogenean gill parasite Discocotyle sagittata Leuckart on Windermere trout, Salmo trutta, L. Parasitology, 55, 667 - 694. Egg hatching in the monogenean gill parasite Discocotyle sagittata from the rainbow trout (Oncorhynchus mykiss). [Extracted from the article]

I dicentrarchi i isolates using testing methods based on those recommended by the Clinical and Laboratory Standard Institute (CLSI). Keywords: antimicrobials; epidemiological cut-off values; minimal inhibitory concentration; Tenacibaculosis; Tenacibaculum dicentrarchi EN antimicrobials epidemiological cut-off values minimal inhibitory concentration Tenacibaculosis Tenacibaculum dicentrarchi 1043 1046 4 06/12/21 20210701 NES 210701 I Tenacibaculum dicentrarchi, i a Gram-negative bacterium, was first described as affecting and causing skin lesions on European seabass ( I Dicentrarchus labrax i ) cultured in Spain (Piñeiro-Vidal et al., 2012). I dicentrarchi i isolates were all wild type to FFC and OTC, except for a single isolate with an FFC MIC of 8.0 µg/ml. I dicentrarchi i isolates were classified as wild type for FFC and OTC. [Extracted from the article]

Proliferative kidney disease (PKD) is a disease found in salmonid fish that is widespread in Europe and North America. The dependency of the clinical signs on the water temperature is extensively reported in rainbow trout, but detailed information on brown trout is lacking. In this study, juvenile brown trout were exposed to the spores of Tetracapsuloides bryosalmonae and then kept at different ambient water temperatures (16°C, 19°C and 22°C) for 10 weeks along with recording of morbidity throughout the experiment. At 6, 8 and 10 weeks post‐exposure, fish from each temperature group were sampled and underwent pathoanatomical examination to survey disease progression. At 16°C, brown trout showed a significantly higher survival probability compared to those kept in 19°C and 22°C water. Additionally, the parasitic burden (MSQ) was higher and the clinical signs were more pronounced in the brown trout kept at 19°C and 22°C compared with the ones kept at 16°C. This study highlights the correlation of PKD outbreaks and water temperature increases related to global climate change, which will impact the future distribution of brown trout in natural waters. [ABSTRACT FROM AUTHOR]

Skin lesions are commonly reported in farmed salmonids. Chinook salmon (Oncorhynchus tshawytscha), introduced from California USA, is the only salmonid species commercially farmed in New Zealand, although trout are cultured for release by Fish and Game New Zealand. There are several farming areas in New Zealand, including Marlborough Sounds, Canterbury and Stewart Island. While the industry has not been affected by any of the major production diseases seen internationally, skin lesions have been recorded with an increase in prevalence from 2012 onwards in the Marlborough Sounds and were associated with elevated summer mortalities on farms in 2015. Here we are proposing case definitions for different types of skin lesions for future monitoring and research. Based on our current understanding of the above skin conditions, we developed case definitions for spots, spreading spots, ulcerated spreading spots and Regular Outline Flank Ulcers defining a positive case for three study units, including individual fish, pen/unit and farm. [ABSTRACT FROM AUTHOR]

Keywords: challenge immersion method; red conger eel; tenacibaculosis EN challenge immersion method red conger eel tenacibaculosis 211 216 6 01/15/21 20210201 NES 210201 Chile has ranked second in salmonid production worldwide since 2010 (Ibieta et al., 2011; Soto et al., 2019), but global aquaculture is trending towards diversification, mainly by farming native species. The aim of this study was to establish whether red conger eel is susceptible and vulnerable to the emerging pathogen I T. dicentrarchi, i which might constitute a sanitary risk for the intensive farming of this fish species. The fish were also verified as not being carriers of and not infected by any Chilean pathogen (e.g. infectious salmon anaemia virus, infectious pancreatic necrosis virus, I Piscirickettsia salmonis i [Avendaño-Herrera, 2011] and pathogens reported in red conger eels [i.e. I Vibrio i spp.]). Our findings indicate that I T. dicentrarchi i QCR41 and QCR29 were pathogenic for adult red conger eels when immersed for 2 hr in an approximate concentration of 3.4 ± 0.3 x 10 SP 4 sp CFU/ml, one logarithm less than that used in Atlantic salmon (Avendaño-Herrera et al., 2016). [Extracted from the article]

Here, we provide evidence that the freshwater parasitic copepod, Salmincola californiensis, acts as a vector for Aeromonas salmonicida. While investigating the effects of S. californiensis on Chinoook salmon (Oncorhynchus tshawytscha), we tangentially observed that fish infected with the copepod developed furunculosis, caused by A. salmonicida. This occurred despite being reared in pathogen-free well water in a research facility with no prior history of spontaneous infection. We further investigated the possibility of S. californiensis to serve as a vector for the bacterium via detection of fluorescently labelled A. salmonicida inside the egg sacs from copepods in which the fish hosts were experimentally infected with GFP-A449 A. salmonicida. We then evaluated copepod egg sacs that were collected from adult Chinook salmon from a freshwater hatchery with A. salmonicida infections confirmed by either culture or PCR. The bacterium was cultured on tryptic soy agar plates from 75% of the egg sacs, and 61% were positive by PCR. These three separate experiments indicate an alternative tactic of transmission in addition to direct transmission of A. salmonicida in captivity. The copepod may play an important role in transmission of the bacterium when fish are more dispersed, such as in the wild., (© 2023 John Wiley & Sons Ltd.)

Piscine orthoreovirus (PRV) is a common and widely distributed virus of salmonids. Since its discovery in 2010, the virus has been detected in wild and farmed stocks from North America, South America, Europe and East Asia in both fresh and salt water environments. Phylogenetic analysis suggests three distinct genogroups of PRV with generally discrete host tropisms and/or regional patterns. PRV‐1 is found mainly in Atlantic (Salmo salar), Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) Salmon of Europe and the Americas; PRV‐2 has only been detected in Coho Salmon of Japan; and PRV‐3 has been reported primarily in Rainbow Trout (Oncorhynchus mykiss) in Europe. All three genotypes can establish high‐load systemic infections by targeting red blood cells for principal replication. Each genotype has also demonstrated potential to cause circulatory disease. At the same time, high‐load PRV infections occur in non‐diseased salmon and trout, indicating a complexity for defining PRV's role in disease aetiology. Here, we summarize the current body of knowledge regarding PRV following 10 years of study. [ABSTRACT FROM AUTHOR]

Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea) is the causative agent of proliferative kidney disease (PKD), which affects both wild and farmed salmonid fish. The objective of this study was to outline differences in susceptibility to PKD in different salmonid species, hybrids and breeding lineages. Susceptibility to T. bryosalmonae infection was established based on cumulative mortality, pathological findings and detection of T. bryosalmonae in the kidney using immunohistochemistry and molecular methods. Determination of pure and hybrid individuals of different species in the genus Salvelinus, and dissimilarity of rainbow trout lineages, was performed using traditional polymerase chain reaction (PCR) and microsatellite analyses. Rainbow trout displayed higher disease severity compared with brook trout and Alsatian charr. Moreover, the results indicated differences in infection susceptibility, not only among different salmonid species but also among different lineages of charr and rainbow trout. Our study indicated that some salmonid species and even different lineages of the same species are more suitable for farming under PKD pressure. [ABSTRACT FROM AUTHOR]

Myxobolus cerebralis (Bivalvulida: Myxobolidae), the aetiological agent of salmonid whirling disease, was detected in 2 river basins of North Carolina during 2015, which initiated the largest spatial–temporal monitoring project for the disease ever conducted within the south‐eastern United States (focused mainly in eastern Tennessee and western North Carolina). A total of 2072 rainbow trout Oncorhynchus mykiss, 1,004 brown trout Salmo trutta and 468 brook trout Salvelinus fontinalis were screened from 113 localities within 7 river basins during June 2017 through October 2019. Infections were detected by pepsin–trypsin digest, microscopy and the species‐specific nested polymerase chain reaction (PCR) in 19 localities across 6 river basins. Myxospore morphology was indistinguishable from the published literature. In 2019, five rainbow trout that symptomatic for whirling disease (sloping neurocranium and lordosis) were captured and processed for histopathology. Myxospores were detected in the calvarial cartilage of two deformed trout with associated erosion of the cartilage consistent with reported whirling disease lesions. This is the first report of M. cerebralis in Tennessee and the first histologically confirmed cases of whirling disease in southern Appalachian (south‐eastern United States) rivers and streams and expands the distribution of M. cerebralis throughout western North Carolina and eastern Tennessee. [ABSTRACT FROM AUTHOR]

To identify the pathogens causing saprolegniosis among farmed fish in Nova Scotia, 172 infected tissues and 23 water samples were collected from six species of teleosts: Atlantic salmon (Salmo salar), brown trout (Salmo trutta), Arctic charr (Salvelinus alpinus), brook trout (Salvelinus fontinalis), striped bass (Morone saxatilis) and rainbow trout (Oncorhynchus mykiss) at nine facilities over a 600 km range. Following laboratory culture, 132 isolates were recovered. Six species of oomycetes were identified from analysis of the internal transcribed spacer (ITS) sequence of the nrDNA: Saprolegnia parasitica, Saprolegnia ferax, Saprolegnia diclina, Saprolegnia aenigmatica, Saprolegnia torulosa, Saprolegnia sp. and Pythiopsis cymosa. Further phylogenetic analyses of the ITS and cytochrome c oxidase subunit 1 (Cox1) regions revealed four strains of Saprolegnia parasitica (named here as S1, S2, S3 and S4), of which S1 and S2 were common (37% and 42% of the isolates), and two strains of S. ferax. Among S. parasitica, S2 and S3 are more closely related to each other than to S1 based on the phylogenetic analyses and predicted RNA secondary structure of the ITS region. Sexual structures with a similar morphology were formed by S1 and S3 in vitro, but were not formed by S2. [ABSTRACT FROM AUTHOR]

In late April 2015, the River Dee Trust informed Marine Scotland Science, Fish Health Inspectorate (FHI), that there had been observations of dead and moribund European eels on the River Dee. Later in May, the Spey Fishery Board also reported a number of moribund European eels in a rotary screw smolt trap on the River Spey. In total, 10 cases involving moribund eels were investigated in 2015 and one case in 2016. In addition, a health screen was conducted to investigate the potential presence of Flavobacterium psychrophilum in healthy eels and Atlantic salmon from the River Dee in 2015. Externally, the diseased eels demonstrated white patches in different locations of the body. In all cases, F. psychrophilum was detected by bacterial isolation and/or molecular methods. Three isolates were further characterized by whole‐genome sequencing (WGS) as belonging to sequence type 15 (ST15). Histological examination of diseased European eels revealed lesions at the level of the integument. The pathogen screen for F. psychrophilum in wild healthy fish tested negative by PCR. Further investigation is required to understand the pathogenicity of this bacterium on the health of eels and the potential impact on the wild salmonid population. [ABSTRACT FROM AUTHOR]

Piscirickettsiosis is the most prevalent bacterial disease affecting seawater salmon in Chilean salmon industry. Antibiotic therapy is the first alternative to counteract infections caused by Piscirickettsia salmonis. The presence of bacterial biofilms on materials commonly used in salmon farming may be critical for understanding the bacterial persistence in the environment. In the present study, the CDC Biofilm Reactor® was used to investigate the effect of sub- and over-MIC of florfenicol on both the pre-formed biofilm and the biofilm formation by P. salmonis under the antibiotic stimuli on Nylon and high-density polyethylene (HDPE) surfaces. This study demonstrated that FLO, at sub- and over-MIC doses, decreases biofilm-embedded live bacteria in the P. salmonis isolates evaluated. However, it was shown that in the P. salmonis Ps007 strain the presence of sub-MIC of FLO reduced its biofilm formation on HDPE surfaces; however, biofilm persists on Nylon surfaces. These results demonstrated that P. salmonis isolates behave differently against FLO and also, depending on the surface materials. Therefore, it remains a challenge to find an effective strategy to control the biofilm formation of P. salmonis, and certainly other marine pathogens that affect the sustainability of the Chilean salmon industry., (© 2023 John Wiley & Sons Ltd.)

A retrospective study was conducted using 250 clinical records of brown trout (Salmo trutta L.) with saprolegniosis by Saprolegnia parasitica, which had been collected from 8 rivers and 1 fish farm in the province of León (Spain). A geographic information system (GIS) was used to obtain skin lesion distribution patterns in males and females. Lesions in wild brown trout affected 15.31 ± 13.33% of the body surface, with a mean of 12.76 ± 6.56 lesions per fish. In addition, 51.23% of wild trout presented lesions with necrosis of the skin or fins. The pattern obtained when not distinguishing between sexes indicated that saprolegniosis lesions are mainly located above the lateral line and most frequently affect the dorsal cephalic region, the adipose fin, the peduncle and the caudal fin. However, differences were observed between males and females. Farmed trout presented a lower percentage of affected body surface (2.06 ± 4.36) and a lower number of lesions with and without necrosis because they received preventive treatment for saprolegniosis. [ABSTRACT FROM AUTHOR]

Vertebral fusions are an established economic concern in farmed Atlantic salmon, but have not been studied in detail in farmed Chinook salmon. Two radiographic studies of vertebral fusions were performed in farmed Chinook salmon. Sixteen of 1,301 (1.2%) smolt and 201 of 2,636 (7.6%) harvest fish had fusions. There were no significant differences in the number of fused vertebrae/fusion in smolt compared with harvest fish. Secondly, tagged fish were repeatedly radiographed to determine the progression of the fusions. Nineteen (4.4%), 23 (5.3%) and 39 (9.0%) fish had fusions as smolt, after 129 days in sea water, and at harvest, respectively. There were no significant differences in the average number of vertebra/fusion between the three time points. Of the fusions that were observed in smolt, additional vertebra did not become fused in 81% of the lesions. Within the rare fusions that did progress due to the involvement of adjacent vertebra, an average of 1.6 vertebrae were added per year. Fish with fusions were significantly lighter than non‐affected fish at harvest. Fusions are common in farmed Chinook salmon; however, they are typically stable after development. As fish with fusions were lighter at harvest, reducing fusions may have an economic benefit. [ABSTRACT FROM AUTHOR]

Infectious haematopoietic necrosis virus (IHNV) is the causative agent of infectious haematopoietic necrosis, a disease of salmonid responsible for great economic losses. The disease occurs in most parts of the world where rainbow trout is reared but has not been previously reported in Kenya. In this study, rainbow trout fry and growers from two farms in Nyeri County were screened for IHNV. Whole fry (n = 4 from each farm) and kidney samples from growers (n = 15 and n = 6 from the two farms, respectively) were collected and preserved for cell culture examination or PCR analysis. Screening of samples was done by PCR followed by sequencing of the glycoprotein gene of the virus. Demonstration of the virus was done by propagation in EPC cells followed by the indirect fluorescence antibody test (IFAT). The results revealed the presence of IHNV at low prevalence of 0.1 and 0.4 for the two farms. The virus was confirmed both by IFAT and by partial sequencing of the G gene. Phylogenetic analysis revealed that the Kenyan isolates were identical to those of the J genogroup found mostly in Asia. The findings have implications for biosecurity measures and import regulations for the Kenyan rainbow trout industry. [ABSTRACT FROM AUTHOR]

Turkey was the largest rainbow trout producer of the European countries in 2016, and the reason for this production is mainly attributed to its egg and fry production. Flavobacterium psychrophilum cause the highest rates of mortality in the starting to feeding stages of the fish. In the present study, twenty‐five F. psychrophilum isolates recovered from rainbow trout, coruh trout and brook trout were analysed by RAPD‐PCR, ERIC‐PCR, REP‐PCR and PCR‐RFLP, including 16S rRNA, gyrA and gyrB gene regions and PCR‐based serotyping method. The PCR‐based molecular analysis showed that the isolates could not be differentiated exactly according to isolation source and geographical region. Most isolates were of type‐1 and type‐2, and some of them were of type‐0 and type‐3; in addition, one isolate showed a unique serotype. The combined analysis results showed that F. psychrophilum isolates discriminated as five different genotypes and all isolates were successfully discriminated based on host. [ABSTRACT FROM AUTHOR]

The use of cleaner fish as a biological control for sea lice in Atlantic salmon aquaculture has increased in recent years. Wild‐caught wrasse are commonly used as cleaner fish in Europe. In Ireland, samples of wrasse from each fishing area are screened for potential pathogens prior to their deployment into sea cages. Salmonid alphavirus was isolated from a pooled sample of ballan wrasse, showing no signs of disease, caught from the NW of Ireland. Partial sequencing of the E2 and nsP3 genes showed that it was closely related to the previously reported SAV subtype 6. This represents only the second isolation of this subtype and the first from a wild fish species, namely ballan wrasse. [ABSTRACT FROM AUTHOR]

Flavobacterium psychrophilum affects many cultured fish species and is considered one of the most important bacterial pathogens causing substantial economic losses in salmonid aquaculture worldwide. Here, F. psychrophilum was identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and nested PCR as the aetiological agent causing mortality in diseased juvenile Siberian sturgeons (Acipenser baerii) reared on a freshwater fish farm. Diseased sturgeons were lethargic and displayed dark skin pigmentation, increased mucus production and the presence of skin ulcerations and haemorrhages specially on the ventral side and the base of fins. The histological examination of fish revealed proliferative branchitis, ulcerative and necrotizing dermatitis and myositis, lymphoid tissue atrophy, liver and kidney degeneration and thrombosis. To the best of our knowledge, this is the first report describing the infection of Siberian sturgeons by F. psychrophilum. The detection of F. psychrophilum in diseased Siberian sturgeons and the description of the pathological findings observed during the outbreak may contribute to a better understanding of the bacterium pathogenicity and the range of fish species susceptible to infection., (© 2023 The Authors. Journal of Fish Diseases published by John Wiley & Sons Ltd.)

Abstract: An epizootic incidence of intestinal adenocarcinomas was reported in brood fish of Atlantic salmon (Salmo salar L.) in 2009. The condition was associated with a specific diet inducing enteritis and morphological changes. Here, two field trials of fish up to slaughter size were initiated. In Trial 1, two different feed recipes were used. Feed I was predominantly based on marine ingredients, whereas plant ingredients were limited to soy protein concentrate and wheat. Feed II was lower in fishmeal and without soya protein, which was substituted with plant proteins from other sources. In Trial 2, a commercial feed (Feed III) was included. No macroscopic tumours were observed in 300 fish (Trial 1). At the end of both trials, samples from five different segments of the gastrointestinal tract of a total of 39 fish were investigated with morphological methods. Here, we show the presence of ectopic proliferating epithelial cells only occurring in inflamed intestine and predominantly in the second segment of the mid‐intestine. Presence of ectopic epithelial cells in submucosal inflammatory foci may indicate early stages in tumorigenesis, but other possibilities such as proliferative enteric disorders cannot be excluded. Together with inflammation, carcinogenesis should be a focus of investigation in future feed trials. [ABSTRACT FROM AUTHOR]

During a 3-month period from June to the end of August 2016, ~5% mortalities were observed in a farm with rainbow trout ( Oncorhynchus mykiss Walbaum) and one farm of common carp ( Cyprinus carpio L.) in Bulgaria. The disease was manifested by gill ulcers/rot, asphyxiation and bloody ascites. Aeromonas hydrophila was isolated from the internal organs of all the diseased fish. Bacillus mycoides or B. pseudomycoides were recovered from the gill lesions on diseased carp and rainbow trout, respectively, with identification achieved by conventional phenotyping and by sequencing of the 16S rRNA gene. In vivo experiments confirmed that all three organisms were pathogenic to rainbow trout. [ABSTRACT FROM AUTHOR]

In 2016, the Norwegian health monitoring programme for wild salmonids conducted a real-time PCR-based screening for salmon gill poxvirus ( SGPV) in anadromous Arctic char ( Salvelinus alpinus L.), anadromous and non-anadromous Atlantic salmon ( Salmo salar L.) and trout ( Salmo trutta L.). SGPV was widely distributed in wild Atlantic salmon returning from marine migration. In addition, characteristic gill lesions, including apoptosis, were detected in this species. A low amount of SGPV DNA, as indicated by high Ct-values, was detected in anadromous trout, but only in fish cohabiting with SGPV-positive salmon. SGPV was not detected in trout and salmon from non-anadromous water courses, and thus seems to be primarily linked to the marine environment. This could indicate that trout are not a natural host for the virus. SGPV was not detected in Arctic char but, due to a low sample size, these results are inconclusive. The use of freshwater from anadromous water sources may constitute a risk of introducing SGPV to aquaculture facilities. Moreover, SGPV-infected Atlantic salmon farms will hold considerable potential for virus propagation and spillback to wild populations. This interaction should therefore be further investigated. [ABSTRACT FROM AUTHOR]

The RIG-I receptors RIG-I, MDA5 and LGP2 are involved in viral recognition, and they have different ligand specificity and recognize different viruses. Activation of RIG-I-like receptors ( RLRs) leads to production of cytokines essential for antiviral immunity. In fish, most research has focused on interferons, and less is known about the production of proinflammatory cytokines during viral infections. In this study, we have cloned the full-length MDA5 sequence in Atlantic salmon, and compared it with RIG-I and LGP2. Further, the salmonid cell line TO was infected with three fish pathogenic viruses, infectious pancreatic necrosis virus ( IPNV), infectious salmon anaemia virus ( ISAV) and salmonid alphavirus ( SAV), and differential gene expression ( DEG) analyses of RLRs, interferons ( IFNa-d) and proinflammatory cytokines ( TNF-α1, TNF-α2, IL-1β, IL-6, IL-12 p40s) were performed. The DEG analyses showed that the responses of proinflammatory cytokines in TO cells infected with IPNV and ISAV were profoundly different from SAV-infected cells. In the two aforementioned, TNF-α1 and TNF-α2 were highly upregulated, while in SAV-infected cells these cytokines were downregulated. Knowledge of virus recognition by the host and the immune responses during infection may help elucidate why and how some viruses can escape the immune system. Such knowledge is useful for the development of immune prophylactic measures. [ABSTRACT FROM AUTHOR]

Rainbow trout, Oncorhynchus mykiss (Walbaum), are able to raise a protective immune response against Aeromonas salmonicida subsp. salmonicida (AS) following injection vaccination with commercial vaccines containing formalin-killed bacteria, but the protection is often suboptimal under Danish mariculture conditions. We elucidated whether protection can be improved by increasing the concentration of antigen (formalin-killed bacteria) in the vaccine. Rainbow trout juveniles were vaccinated by intraperitoneal (i.p.) injection with a bacterin of Aeromonas salmonicida subsp. salmonicida strain 090710-1/23 in combination with Vibrio anguillarum serotypes O1 and O2a supplemented with an oil adjuvant. Three concentrations of AS antigens were applied. Fish were subsequently challenged with the homologous bacterial strain administered by perforation of the tail fin epidermis and 60-s contact with live A. salmonicida bacteria. The infection method proved to be efficient and could differentiate efficacies of different vaccines. It was shown that protection and antibody production in exposed fish were positively correlated to the AS antigen concentration in the vaccine. [ABSTRACT FROM AUTHOR]

Tenacibaculosis is an emerging disease that severely affects salmonid farming in Chile, producing high mortalities and causing great economic losses. This work describes a novel PCR assay for the specific detection of Tenacibaculum piscium, a species recently described and identified in tenacibaculosis outbreaks in Norway and Chile. The designed primers amplified a 678-bp fragment of the peptidase gene (peptidase M23 family) from T. piscium. This method is specific for T. piscium; no other chromosomal DNA amplification products were obtained for other Tenacibaculum species. In pure cultures, the PCR assay detected up to 500 pg of DNA, or the equivalent of 2.44 ± 0.06 × 10 4  CFU/ml. For seeded fish samples (i.e., gills, liver, kidney, and mucus), the sensitivity limit was 4.88 ± 0.11 × 10 6  CFU/g, sufficient to detect T. piscium in acute infections in fish. Notably, this sensitivity level was 100-fold lower for DNA extracted from mucus samples. As compared to other existing methodologies (e.g., gene sequencing), the PCR approach described in this work allowed for the easiest detection of T. piscium in mucus samples obtained from challenged fish, an important outcome considering that the identification of this bacterium is difficult. Our results indicate that the designed specific primers and PCR method provide a rapid and specific diagnosis of T. piscium., (© 2023 John Wiley & Sons Ltd.)

Triploid Atlantic salmon populations are associated with higher prevalence of lower jaw skeletal anomalies affecting fish performance, welfare and value deleteriously. Anomalous lower jaw can be curved downward ( LJD), shortened ( SJ) or misaligned ( MA). Two separate groups of triploid Atlantic salmon (~12 g) with either normal lower jaw ( NOR) or SJ were visually assessed four times over three months for presence and concurrence of jaw anomalies (with severity classified) and opercular shortening to understand the relatedness of these anomalous developmental processes. The prevalence of jaw anomalies increased in both groups over time ( NOR group - SJ, LJD and MA combined 0-24.5%; SJ group - LJD and MA combined 17-31%). SJ and LJD occurred both independently and concurrently whereas MA exclusively concurred with them. All three anomalies could be concurrent. Severity of both LJD and SJ increased in the SJ group only. Opercular shortening recovery was observed in both groups but at a slower rate in the SJ group. The SJ group specific growth rate ( SGR) was significantly ( P < 0.05) lower than the NOR group. This study demonstrated the concurrence of SJ, LJD and MA and showed possible deleterious consequences deriving from the conditions. [ABSTRACT FROM AUTHOR]

In relation to stock enhancement programmes, wild salmon broodfish have been routinely screened for the presence of Renibacterium salmoninarum antigens (Rs-Ag) for decades. A sudden increase in the prevalence of Rs-Ag experienced caused extensive problems to this industry as eggs from positive fish are discarded. The prevalence and level of Rs-Ag were examined in resident and anadromous salmonids in the River Ellidaár system and the progress of Rs-Ag in a cohort of salmon followed. Both prevalence and Rs-Ag levels were high in resident salmonids and emigrating salmon smolts in the river system. When the smolts re-entered their home river as adults the following summer, they were almost free of Rs-Ag, but the longer they stayed in the river, the more Rs-Ag they acquired; the majority being positive at spawning. This study demonstrates a high level of Rs-Ag in salmonids in the River Ellidaár system which significantly reduces in the salmon during its seawater phase. Accordingly, it seems ideal to sample salmon broodfish as soon as possible after ascending the river and subsequently transfer to Rs-free environment for storage until stripping, which could result in lower Rs-prevalence and minimize the problems that stock enhancement programmes have faced due to Rs-positive wild broodfish. [ABSTRACT FROM AUTHOR]

The article discusses two studies on piscine orthoreovirus in nonanadromous salmonids in Norway. The study reportedly involved brown trout and landlocked salmon which spend their entire life in freshwater and did not come in contact with seawater migrating salmonids. The study revealed a lack of evidence of significant piscine orthoreovirus in freshwater reservoirs.

The article presents the results of a study that evaluated in vivo the adjuvant activity of Filifolinone in Atlantic salmon spiked with formulations developed from bacterins of P. salmonis, along with the extraction of Filifolinone from Heliotropium sclerocarpum Phil. Bacterin was prepared from P. salmonis inactivated using formalin, which was mixed with Montanide or Filifolinone. Salmonids vaccinated with P. salmonis bacterins worsened the disease due to immunosuppressive antigens.

The article presents a study which demonstrate a functional alphavirus replicon encoding b-Gal protein and its ability to induce immune response in salmonids. Fish rearing and experimentation were performed while immune responses were evaluated in the study. Results in the study demonstrated the capability of the intramuscular administration of Semliki Forest virus (SFV)-based construct in delivering antigen to the immune system of salmonids under cold water conditions.

The article discusses the use of quinolones as the antimicrobial compounds against salmonid rickettsial septicaemia (SRS) in Chile. It states that quinolones susceptibility was assessed in 20 P. salmonis isolates cultured from kidney samples of diseased fish collected from diverse geographic origin from 2010-2012. It mentions the hypothesis that Chilean quinolone-resistant P. salmonis isolates may have mutations on their Quinolone Resistance-Determining Region (QRDR).

A challenge model for pancreas disease in Atlantic salmon, Salmo salar L. fry, was developed comparing two salmonid alphavirus ( SAV) subtypes: SAV1 and SAV5. Viral doses of 3 × 105 TCID50 mL−1 for SAV1 and 3 × 104 for SAV5 were tested in triplicate tanks, each containing 450 salmon fry. Cumulative mortalities of 1.2% were recorded. Titres of virus recovered from the mortalities ranged from 102 to 107 TCID50 mL−1. Fry were sampled at 3, 5 and 7.5 weeks post-challenge. Sampling after 3 weeks revealed a high prevalence of infection in the absence of clinical signs, and infectious virus was recovered from 80% and 43% of sampled fry infected with SAV1 and SAV5, respectively. After 5 weeks pancreas, heart and red skeletal muscle lesions were generally observed, whilst degeneration in white skeletal muscle was observed only in fish infected with SAV1. In situ hybridisation confirmed the presence of viral genome in infected pancreas, heart and muscle. After 7.5 weeks, infectious virus (both isolates) was recovered from 13.3% of the fish sampled, with a viral titre of 102 TCID50 mL−1. Clearly, salmon fry are susceptible to SAV infection and pancreas disease. [ABSTRACT FROM AUTHOR]

Slovenia has no history of health problems related to proliferative kidney disease ( PKD) either in farmed or in wild fish. However, due to the past molecular evidence for the presence of Tetracapsuloides bryosalmonae DNA in tissues of some fish from open waters, a survey was conducted on wild salmonids that were primarily sampled for other purposes. In winter 2010-2011, specimens from a total of 244 rainbow trout, Oncorhynchus mykiss ( Walbaum), and brown trout, Salmo trutta L., from 30 bodies of fresh water were examined for T. bryosalmonae using a PCR method. The sampled fish showed no clinical signs or gross pathological lesions characteristic of PKD. Nineteen (7.8%) fish from seven (23.3%) fresh waters were positive for T. bryosalmonae. The identity of PCR amplicons was confirmed by sequencing. With one exception, all the positive fish were found in waters from the regions where the average yearly temperatures and the environmental pollution are higher. This preliminary countrywide survey provided the first insight into the situation regarding T. bryosalmonae infection of wild salmonids in Slovenia. [ABSTRACT FROM AUTHOR]

The serological reactivity between strains of each of the six currently genetically defined subtypes of salmonid alphavirus ( SAV) was examined by comparison of homologous and heterologous virus neutralization titres on sera from experimentally infected fish. With the exception of the level of SAV subtype 6 neutralization by heterologous sera, good cross-neutralization was detected between all subtypes, albeit with variation in geometric mean titres when each subtype-specific serum set was tested against the panel of virus subtypes. A similar pattern was evident with field sera, except that heterologous neutralization of the SAV6 strain was more evident. In only 23% of available pairwise comparisons was the homologous titre recorded with an experimentally derived serum fourfold or greater than the heterologous titre, and in only two instances was this difference demonstrated in both directions. No virus strains consistently met the old serology-based criteria (Sub-committee on Inter-relationships Among Catalogued Alphaviruses) to be considered separate subtypes within an alphavirus species. Only when testing with an SAV subtype-2-specific monoclonal antibody was a major difference between homologous and heterologous neutralization capacity evident. These results provide new direct or indirect information in terms of SAV classification, vaccine efficacy and the selection and validation of reagents for serological and immunological diagnostic purposes. [ABSTRACT FROM AUTHOR]

One hundred farmed Atlantic salmon, Salmo salar L., were examined for the presence of nematodes by digestion of tissue in HCl-pepsin solution. All fish were sampled from one cage in a fish farm on the Norwegian south-west coast. Fifty harvest quality salmon, that is, salmon for human consumption (mean 5.4 kg, variation 3.0-7.6 kg), were sampled at the processing line while 50 salmon runts (mean 1.1 kg, variation 0.4-1.8 kg), discarded due to poor performance, were sampled from the discard bin after the grading station. Runts are individual fish with clear signs of poor performance over time and abnormal appearance and are thus not processed for human consumption. No nematodes were found in the musculature or viscera of the 50 harvest quality salmon. In total, 75 nematodes were found in 10 (20%) of the runts; 53 nematodes in the viscera and 22 in the musculature. Nematodes in the musculature were identified as Anisakis simplex ( Rudolphi, 1809 det. Krabbe, 1878), while nematodes in the viscera were identified as A. simplex and Hysterothylacium aduncum ( Rudolphi, 1802). [ABSTRACT FROM AUTHOR]

Michigan's fisheries rely primarily upon the hatchery propagation of salmonid fish for release in public waters. One limitation on the success of these efforts is the presence of bacterial pathogens, including Aeromonas salmonicida, the causative agent of furunculosis. This study was undertaken to determine the prevalence of A. salmonicida in Michigan fish, as well as to determine whether biochemical or gene sequence variability exists among Michigan isolates. A total of 2202 wild, feral and hatchery-propagated fish from Michigan were examined for the presence of A. salmonicida. The examined fish included Chinook salmon, Oncorhynchus tshawytscha (Walbaum), coho salmon, O. kisutcha (Walbaum), steelhead trout, O. mykiss (Walbaum), Atlantic salmon, Salmo salar L., brook trout, Salvelinus fontinalis (Mitchill), and yellow perch, Perca flavescens (Mitchill). Among these, 234 fish yielded a brown pigment-producing bacterium that was presumptively identified as A. salmonicida. Further phenotypic and phylogenetic analyses identified representative isolates as Aeromonas salmonicida subsp. salmonicida and revealed some genetic and biochemical variability. Logistic regression analyses showed that infection prevalence varied according to fish species/strain, year and gender, whereby Chinook salmon and females had the highest infection prevalence. Moreover, this pathogen was found in six fish species from eight sites, demonstrating its widespread nature within Michigan. [ABSTRACT FROM AUTHOR]

Farmed and wild salmonids are affected by a variety of skin conditions, some of which have significant economic and welfare implications. In many cases, the causes are not well understood, and one example is cold water strawberry disease of rainbow trout, also called red mark syndrome, which has been recorded in the UK since 2003. To date, there are no internationally agreed methods for describing these conditions, which has caused confusion for farmers and health professionals, who are often unclear as to whether they are dealing with a new or a previously described condition. This has resulted, inevitably, in delays to both accurate diagnosis and effective treatment regimes. Here, we provide a standardized methodology for the description of skin conditions of rainbow trout of uncertain aetiology. We demonstrate how the approach can be used to develop case definitions, using coldwater strawberry disease as an example. [ABSTRACT FROM AUTHOR]

The freshwater bryozoan Fredericella sultana ( Blumenbach) is the most common invertebrate host of the myxozoan parasite Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease in salmonid fish. Culture media play an important role in hatching of statoblasts and maintaining clean bryozoan colonies for Malacosporea research. We developed a novel culture medium, Bryozoan Medium C ( BMC), for the cultivation and maintenance of F. sultana under laboratory conditions. Statoblasts of F. sultana were successfully hatched to produce transparent-walled, specific pathogen-free ( SPF) colonies that were maintained >12 months in BMC at pH 6.65. Tetracapsuloides bryosalmonae was successfully transmitted from infected brown trout, Salmo trutta L., to newly hatched F. sultana colonies in BMC, then from the infected bryozoan to SPF brown trout. This study demonstrated the utility of BMC ( pH 6.65) for hatching statoblasts, long-term cultivation of clean and transparent bryozoan colonies and maintenance of the Tetracapsuloides bryosalmonae life cycle in the laboratory for molecular genetic research and other studies such as host-parasiteinteraction. [ABSTRACT FROM AUTHOR]

The article focuses on a study for the detection of subtype 2-related salmonid alphavirus (SAV2)-related virus in Norway. The Norwegian Veterinary Institute (NVI) got formalin-fixed tissues from Atlantic salmon of approximately 4.5 kg in 2011. SAV was found in 12 of 20 fish, indicating low amounts of virus.

Tenacibaculosis caused by Tenacibaculum dicentrarchi is the third most important bacterial fish infection affecting the Chilean salmon industry. Losses to this disease are most frequently controlled by treatments with florfenicol and oxytetracycline. However, recent tenacibaculosis outbreaks were controlled through the extra-label, oral administration of tiamulin, resulting in high treatment efficiency. In this study, we present an analysis of susceptibility patterns of 32 T. dicentrarchi isolates and the type strain CECT 7612 T to tiamulin by determining the minimum inhibitory concentrations (MICs) according to the procedures recommended by the Clinical and Laboratory Standard Institute, but fixing incubation temperature to the more appropriate for the growth of T. dicentrarchi (18 ºC). The MICs of the T. dicentrarchi isolates were unimodally distributed (0.06-1.0 µg/ml range), while the CECT 7612 T strain presented an MIC of 0.5 μg/ml. Calculations using Normalized Resistance Interpretation provided epidemiological cut-off values of ≤1.0 µg/ml, with the 33 T. dicentrarchi classified as wild type. In Chile, tiamulin is authorized for use in other livestock species, but application in salmonids is extra-label. Our presented in vitro results suggest that tiamulin is a viable alternative to florfenicol, specifically as tiamulin requires comparatively lower concentrations to inhibit T. dicentrarchi. Considering that tiamulin is also exclusively for veterinary use, is classified as "least important" by the World Health Organization and has not resulted in the development of bacterial resistance, pharmaceutical companies should be requested to register tiamulin and provide alternative antimicrobial treatments for the salmonid industry., (© 2022 John Wiley & Sons Ltd.)

Bacterial kidney disease (BKD) can be a devastating bacterial infection in salmonids, and it is present in aquaculture throughout the world. BKD is caused by the Gram-positive facultative intracellular bacterium Renibacterium salmoninarum (R. salmoninarum) that is spread both horizontally and vertically. Disease signs include external ulcerations and blisters and internal signs such as organ swelling, granulomas, petechiae and ascites. In Sweden, BKD accounts for a significant income loss in aquacultures due to expensive decontamination of the facility and increased disease susceptibility for the immunocompromised fish leading to higher mortality rates. In addition, uncontrolled spread in aquaculture may threaten the survival of wild fish populations. The aim of our study was to investigate the prevalence of R. salmoninarum in wild salmonids caught in Swedish waters where net pen farms with a recent history of BKD are present. Four rivers with at least one BKD-positive or recently BKD-positive farm were selected. In addition, we evaluated the use of environmental DNA (eDNA) for surveillance and monitoring of ongoing infections at these locations. In total, 1058 fish were sampled from four different river systems, and of them 52 (4.9%) were positive for R. salmoninarum by antigen ELISA. Surprisingly, these fish were not evenly distributed between the four river systems, but 50 were caught in the same river (Ljungan). This accounts for an alarmingly high rate of 17% R. salmoninarum-positive samples in wild salmonids in this area. This number is far above what was expected and clearly shows the risk with an open farming system as well as the importance of effective health monitoring programmes to avoid an uncontrolled spread of the disease. The use of eDNA for monitoring BKD is somewhat difficult to evaluate. Few of the water samples analysed were PCR positive for R. salmoninarum (2 of 38) and those were collected where no ELISA positive fish were identified. In addition to water, sediment samples were collected under a net pen farm that had recently slaughtered all fish due to ongoing R. salmoninarum infections. Sediment samples are more promising than water as 4 of 5 samples at one farming facility where positive for R. salmoninarum. Thus, sediment samples may be valuable for monitoring potential ongoing BKD in farms, without the need to sacrifice valuable fish., (© 2022 The Authors. Journal of Fish Diseases published by John Wiley & Sons Ltd.)

Sequence data from salmonid alphavirus (SAV) strains obtained from farmed marine Atlantic salmon, Salmo salar L. , over a 20-year period between 1991 and 2011 was reviewed to examine the geographical distribution of the genetically defined SAV subtypes in twelve regions across Ireland and Scotland. Of 160 different Atlantic salmon SAV strains examined, 62 belonged to subtype 1, 28 to subtype 2, 34 to subtype 4, 35 to subtype 5 and 1 to subtype 6. SAV subtypes 1, 4 and 6 were found in Ireland, while subtypes 1, 2, 4 and 5 were found in Scotland. In the majority of regions, there was a clear clustering of subtypes, with SAV subtype 1 being the dominant subtype in Ireland overall, as well as in Argyll and Bute in Scotland. SAV subtype 2 predominated in the Shetland and Orkney Islands. The emergence in Atlantic salmon of subtype 2 strains typically associated with sleeping disease in rainbow trout in Argyll and Bute, strongly suggesting transmission of infection between these species, was noted for the first time. SAV subtype 4 was the most common subtype found in the southern Western Isles, while SAV subtype 5 predominated in the northern Western Isles and north-west mainland Scotland. No single strain was dominant on sites in the western Highlands, with a number of sites in this region in particular having more than one subtype detected in different submissions. The significance of these results in relation to aspects of the epidemiology of infection, including transmission, biosecurity and wildlife reservoirs are discussed and knowledge gaps identified. [ABSTRACT FROM AUTHOR]

The development and the application of a quantitative duplex real-time PCR for the detection of Neoparamoeba perurans and the elongation factor α 1 gene (ELF) of Atlantic salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), are described. A set of primers and probe was designed to amplify a 139-bp fragment specific to the N. perurans 18S rRNA gene. The test was shown to be very sensitive, being able to detect as little as 13.4 DNA copies per μL corresponding to 0.15 fg of template DNA. In addition, the reaction that detected N. perurans was found to have a high degree of repeatability and reproducibility, to have a linear dynamic range ( R2 = 0.999) extending over 5 log10 dilutions and to have a high efficiency (104%). The assay was applied to DNA samples extracted from 48 formalin-fixed, paraffin-embedded (FFPE) salmon gill tissues showing varying degrees of gill histopathology and amoebic gill disease (AGD)-type histopathology ranging from absent to severe (each scored 0-3). Neoparamoeba perurans DNA was detected in all the blocks where AGD-type histopathology was diagnosed microscopically and in 43.6% of the blocks showing signs of gill pathology. The association between parasitic load and gill histopathology and AGD-type histopathology severity was also investigated. This study also describes the development and the application of a second real-time PCR for the generic detection of Neoparamoeba spp ., Page, 1987. A set of primers and probe conserved among the Neoparamoeba spp. was designed to amplify a 150-bp fragment within the 18S rRNA gene. Applied to N. perurans-negative gill tissues, the method was used to exclude the presence of other Neoparamoeba spp. in those blocks where gill pathology was observed microscopically. [ABSTRACT FROM AUTHOR]

Yersiniosis (enteric red mouth disease) is a contagious bacterial disease caused by Yersinia ruckeri, which primarily affects salmonids. A real-time PCR assay using a molecular beacon has been developed and validated to improve the detection of the causative biotypes of Y. ruckeri. The assay, which targets the glnA (glutamine synthetase) gene, proved to have 100% analytical specificity and analytical sensitivities of 5 fg and 3 × 103 CFU g−1 for DNA and seeded kidney tissue, respectively. The assay was highly repeatable with low % CV for intra- and inter-run experiments, and the optimized parameters transferred easily between different real-time PCR platforms. Following analytical validation, diagnostic specificity was determined using New Zealand farmed Chinook salmon ( n = 750) from 10 farms during 2007/08. The real-time PCR was run in parallel with the bacterial culture detection method, and all fish tested were found to be negative by both methods for Y. ruckeri, resulting in 100% diagnostic specificity (95% confidence interval). The molecular beacon real-time PCR system is specific, sensitive, reproducible and a rapid method for the detection of Y. ruckeri and has the potential to be used for routine diagnostic testing, health certification and active surveillance programmes. [ABSTRACT FROM AUTHOR]