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Aeromonas salmonicida, a widely distributed aquatic pathogen causing furunculosis in fish, exhibits varied virulence, posing challenges in infectious disease and immunity studies, notably in vaccine efficacy assessment. Lumpfish (Cyclopterus lumpus) has become a valuable model for marine pathogenesis studies. This study evaluated several antigen preparations against A. salmonicida J223, a hypervirulent strain of teleost fish, including lumpfish. The potential immune protective effect of A. salmonicida bacterins in the presence and absence of the A‐layer and extracellular products was tested in lumpfish. Also, we evaluated the impact of A. salmonicida outer membrane proteins (OMPs) and iron‐regulated outer membrane proteins (IROMPs) on lumpfish immunity. The immunized lumpfish were intraperitoneally (i.p.) challenged with 104A. salmonicida cells/dose at 8 weeks‐post immunization (wpi). Immunized and non‐immunized fish died within 2 weeks post‐challenge. Our analyses showed that immunization with A. salmonicida J223 bacterins and antigen preparations did not increase IgM titres. In addition, adaptive immunity biomarker genes (e.g., igm, mhc‐ii and cd4) were down‐regulated. These findings suggest that A. salmonicida J223 antigen preparations hinder lumpfish immunity. Notably, many fish vaccines are bacterin‐based, often lacking efficacy evaluation. This study offers crucial insights for finfish vaccine approval and regulations. [ABSTRACT FROM AUTHOR]

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., (© 2025 John Wiley & Sons Ltd.)

In recent years, the use of cleaner fish for biological control of sea lice has increased considerably. Along with this, a number of infectious diseases have emerged. The aim of this study was to investigate the susceptibility of lumpfish (Cyclopterus lumpus) to Betanodavirus since it was detected in asymptomatic wild wrasses in Norway and Sweden. Three betanodaviruses were used to challenge lumpfish: one RGNNV genotype and two BFNNV genotypes. Fish were injected and monitored for 4 weeks. Brain samples from clinically affected specimens, from weekly randomly selected fish and survivors were subjected to molecular testing, viral isolation, histopathology and immunohistochemistry. Reduced survival was observed but was attributed to tail‐biting behaviour, since no nervous signs were observed throughout the study. Betanodavirus RNA was detected in all samples, additionally suggesting an active replication of the virus in the brain. Viral isolation confirmed molecular biology results and revealed a high viral titre in BFNNV‐infected groups associated with typical lesions in brains and eyes of survivor fish. We concluded that lumpfish are susceptible to Betanodavirus, as proven by the high viral titre and brain lesions detected, but further studies are necessary to understand if Betanodavirus can cause clinical disease in this species. [ABSTRACT FROM AUTHOR]

Lumpfish (Cyclopterus lumpus), a native fish of the North Atlantic Ocean, is utilized as cleaner fish to biocontrol sea lice infestations in Atlantic salmon aquaculture. However, bacterial infections are affecting cleaner fish performance. Vibrio anguillarum, the aetiological agent of vibriosis, is one of the most frequent bacterial infections in lumpfish, and effective vaccine programmes against this pathogen have been identified as a high priority for lumpfish. Vibrogen‐2 is a commercial polyvalent bath vaccine that contains formalin‐inactivated cultures of V. anguillarum serotypes O1 and O2, and Vibrio ordalii. In this study, we evaluated Vibrogen‐2 efficacy in lumpfish against a local isolated V. anguillarum strain. Two groups of 125 lumpfish were bath‐immunized, bath‐boost‐immunized at four weeks post‐primary immunization, and intraperitoneally (i.p.) boost‐immunized at eight weeks post‐primary immunization. The control groups were i.p. mock‐immunized with PBS. Twenty‐seven weeks post‐primary immunization, the fish were i.p. challenged with 10 or 100 times the V. anguillarum J360 LD50 dose. After the challenge, survival was monitored daily, and samples of tissues were collected at ten days post‐challenge. Commercial vaccine Vibrogen‐2 reduced V. anguillarum tissue colonization and delayed mortality but did not confer immune protection to C. lumpus against the V. anguillarum i.p. challenge. [ABSTRACT FROM AUTHOR]

Samples from moribund lumpfish were collected in a marine hatchery in Scotland in 2015. Black nodules were noted on the skin, and gills and fungal hyphae were extensively distributed in musculature and internal organs. Multifocal chronic inflammatory lesions displaced structures in all affected organs. Mortalities commenced on completion of spawning in May and were evenly distributed over the second year in the temperature range 11–15°C. The main systemic infection causing agent was initially identified based on morphological characteristics as an Exophiala species. Ribosomal DNA (rDNA) ITS regions of the isolates were subsequently sequenced confirming the isolates belonged to Exophiala genus. All isolates fell in a single phylogenetic cluster, which is represented by Exophiala angulospora. Fish were treated with either formalin or Bronopol or a combination of both, but there was no effect on the pattern or numbers of mortalities. Isolates were also tested against three different concentrations of Latrunculin A, Amphotericin B and Itraconazole with no success. It is of utmost importance to increase the knowledge on pathogen–host interactions to successfully develop sustainable control methods. [ABSTRACT FROM AUTHOR]

The incidence of disease caused by Pasteurella sp. in farmed lumpsuckers in Norway has been steadily increasing in recent years, causing significant economic losses and fish welfare issues. The disease affects all life stages, both in hatcheries and after release into salmon cages. Therefore, it is important to establish robust challenge models, to be used for vaccine development. Exposure experiments via intramuscular and intraperitoneal injection underlined the high virulence of the bacteria, whereas the cohabitation and bath models allowed the chronic symptoms of the disease to be studied more accurately. Skin lesions and haemorrhage at the base of fins were observed in the more acute cases of the disease. Symptoms including white spots over the skin, especially around the eyes, characterized the chronic cases. The latter were most prominent from the bath challenge model. Histopathology indicated a systemic pattern of disease, whereas qPCR analysis from head kidney showed that bacteria may be present in survivor fish at the end of the challenges. In all the challenge models investigated, Pasteurella sp. was re‐isolated from the fish, thus fulfilling Koch's postulates. These findings highlight the importance of screening of lumpsuckers prior to transfer to minimize the risks of carrying over asymptomatic carriers. [ABSTRACT FROM AUTHOR]

A novel viral haemorrhagic septicaemia virus (VHSV) of genotype IV was isolated from wild lumpfish (Cyclopterus lumpus), brought to a land‐based farm in Iceland, to serve as broodfish. Two groups of lumpfish juveniles, kept in tanks in the same facility, got infected. The virus isolated was identified as VHSV by ELISA and real‐time RT‐PCR. Phylogenetic analysis, based on the glycoprotein (G) gene sequences, may indicate a novel subgroup of VHSV genotype IV. In controlled laboratory exposure studies with this new isolate, there was 3% survival in the I.P. injection challenged group while there was 90% survival in the immersion group. VHSV was not re‐isolated from fish challenged by immersion. In a cohabitation trial, lumpfish infected I.P. (shedders) were placed in tanks with naïve lumpfish as well as naïve Atlantic salmon (Salmo salar L.). 10% of the lumpfish shedders and 43%–50% of the cohabiting lumpfish survived after 4 weeks. 80%–92% of the Atlantic salmon survived, but no viral RNA was detected by real‐time RT‐PCR nor VHSV was isolated from Atlantic salmon. This is the first isolation of a notifiable virus in Iceland and the first report of VHSV of genotype IV in European waters. [ABSTRACT FROM AUTHOR]

Winter ulcer disease, caused by Moritella viscosa, is a significant problem in cold water salmonid farming, although the bacterium can infect and cause disease in a number of other fish species, such as lumpfish (Cyclopterus lumpus). Lumpfish are used as cleaner fish, to eat sea lice from Atlantic salmon (Salmo salar) in sea pens. It remains to be established whether M. viscosa can be transmitted between the fish species. In this study, we examined whether a salmon isolate of M. viscosa could infect and cause disease in lumpfish. We further examined whether a lumpfish isolate of M. viscosa could infect and cause disease in salmon. Finally, we examined whether vaccination of salmon with a salmon isolate of M. viscosa conferred protection against a lumpfish isolate. The data indicate that while lumpfish appeared to be resistant to a salmon isolate of M. viscosa, the salmon could be infected with a lumpfish isolate of M. viscosa. Vaccination protected the salmon against the salmon isolate of M. viscosa but did not confer sufficient protection to prevent infection with the lumpfish isolate. [ABSTRACT FROM AUTHOR]

Aeromonas salmonicida strains are roughly classified into two categories, typical and atypical strains. The latter mainly regroup isolates that present unusual phenotypes or hosts, comparatively to the typical strains that belong to the salmonicida subspecies. This study focuses on an uncharacterized atypical strain, M18076-11, isolated from lumpfish (Cyclopterus lumpus) and not part of the four recognized Aeromonas salmonicida subspecies. This isolate presents an unreported phenotype in the A. salmonicida species: the formation of large granular aggregates. Granules are formed of a heterogeneous mix of live and dead cells, with live cells composing the majority of the population. Even if no mechanism was determined to cause cellular aggregation, small globular structures at the cell surface were observed, which might affect granular formation. Pan-genome phylogenetic analysis indicated that this strain groups alongside the masoucida subspecies. However, phenotypic tests showed that these strains have diverging phenotypes, suggesting that M18076-11 might belong to a new subspecies. Also, a pAsal1-like plasmid, which was only reported in strains of the subspecies salmonicida, was discovered in M18076-11. This study sheds light on unsuspected diversity in A. salmonicida subspecies and stresses the need of thorough identification when a new strain is encountered, as unique traits might be discovered. [ABSTRACT FROM AUTHOR]

We present a study on the effect of water temperature on immunization of Atlantic lumpfish. In total, 360 fish were vaccinated with either 50 μl of an oil-based injection vaccine (VAX), with Aeromonas salmonicida and Vibrio salmonicida antigens, or PBS. Fish were vaccinated at three different water temperatures, 5°C, 10°C and 15°C, and sorted into six groups (N = 60). Lumpfish were weighed every 3 weeks after vaccination, sampled at 3, 6, 9 and 18 weeks post-immunization (wpi) and evaluated by modified Speilberg score, ELISA and immunoblotting. Vaccinated fish showed low antibody response against V. salmonicida. Fish vaccinated at 5°C showed significantly lower antibody response against A. salmonicida throughout the study. At higher temperatures, vaccinated fish showed significantly increased antibody responses, at 18 wpi for 10°C and at 6 and 18 wpi for 15°C. Immunoblotting demonstrated specific response against the LPS antigen of A. salmonicida in the 10°C and 15°C VAX groups. Mean body weight increased in all groups throughout the study. Vaccinated fish had low Speilberg scores with no melanization of abdominal tissue. Our results show that vaccinating lumpfish at a lower water temperature may lead to a low antibody response against A. salmonicida. [ABSTRACT FROM AUTHOR]

Atlantic lumpfish ( Cyclopterus lumpus L.) is used as a biological delousing agent for sea lice ( Lepeophtheirus salmonis K.) infestations in Norwegian aquaculture. Here, we present a study on the antibody response and vaccine side effects after intramuscular and intraperitoneal injection of lumpfish with two vaccines. Both vaccines contained bacterial antigens from atypical Aeromonas salmonicida A-layer types V and VI, Vibrio anguillarum serotype O1 and Moritella viscosa sp., but one vaccine contained a vegetable oil-based adjuvant, while the other contained a mineral oil-based adjuvant. Intramuscular injection of the mineral oil-based vaccine caused a high acute mortality of fish within 48 hr after immunization. Intraperitoneal injection of the mineral oil-based vaccine resulted in a lower severity of intra-abdominal side effects than the vegetable oil-based vaccine. Intramuscular injection of the mineral oil-based vaccine resulted in a significantly higher antibody response against A. salmonicida when compared to controls and the vegetable oil-based vaccine group. The antibody response was poor against V. anguillarum and M. viscosa for all groups. Our results indicate that intramuscular injection of oil-based vaccines might be feasible for providing immunological protection for Atlantic lumpfish against bacterial diseases, especially atypical A. salmonicida, but more work is required to identity optimal adjuvants. [ABSTRACT FROM AUTHOR]

Twelve groups of farmed lumpfish and one of wild lumpfish were screened for cataract and sampled for fish muscle tissue, whole heart and both eye lenses to investigate possible relations between cataract and tissue free amino acid concentrations. Cataract prevalence ranged from 20% to 100%, with the highest average score of 7.3 (max 8) and incidences of severe cataract (>5) in all groups. Cataract could not be explained by suboptimal histidine concentrations in the feed. Neither muscle nor cardiac tissues had concentrations of free histidine compounds. The lumpfish lens contained N-acetylhistidine ( NAH), of which low concentrations were strongly related to cataract severity. However, no correlation between lens NAH and cataract severity was found in the present sample set. Wild lumpfish had higher levels compared to farmed lumpfish, suggesting that the farmed lumpfish may have been deficient in histidine or have a higher utilization of NAH due to osmotic problems. Thus, cataract in farmed lumpfish may be related to primary or secondary disturbed nutrient metabolism or malnutrition, shown by the high levels of specific amino acids in different tissues, which may cause osmotic imbalance and cataract development. This nutritional or environmental-related welfare problem deserves further research. [ABSTRACT FROM AUTHOR]

A Piscirickettsia salmonis infection was diagnosed in lumpfish ( Cyclopterus lumpus L.) juveniles held in a marine research facility on the west coast of Ireland. The main clinical signs and pathology included marked ascites, severe multifocal liver necrosis and severe diffuse inflammation and necrosis of the exocrine pancreas and peri-pancreatic adipose tissue. Numerous Piscirickettsia-like organisms were observed by histopathology in the affected organs, and the bacterial species was characterized by molecular analysis. Sequencing of the partial 16S rDNA gene and internal transcribed spacer region showed the lumpfish sequences to be closely related to previously identified Atlantic salmon ( Salmo salar L.) sequences from Ireland. To the authors' knowledge, this is the first detection of P. salmonis in lumpfish worldwide. The infection is considered potentially significant in terms of lumpfish health and biosecurity. [ABSTRACT FROM AUTHOR]

A microsporidian species with 98.3-98.4% nucleotide identity to Tetramicra brevifilum ( Journal of Fish Diseases, 3, 1980, 495) was diagnosed in lumpfish ( Cyclopterus lumpus, L.) broodstock held at a breeding and rearing facility in western Ireland. The fish were wild-caught from the west coast of Ireland, and the first case was diagnosed one year after capture. Clinical signs included severe bloating, lethargy, exophthalmos, anorexia, white patches on the cornea and externally visible parasitic cysts on skin and fins. Necropsy revealed severe ascites, white nodules and vacuoles in all the internal organs and partial liquefaction of the skeletal muscle. On histological examination, microsporidian xenomas were observed in all internal organs, the skin, skeletal muscle, gills and the eyes. The microsporidian species was identified by molecular analysis and transmission electron microscopy. This is the first record of T. brevifilum infecting lumpfish, and the disease is considered to be of potential significance to the rising aquaculture industry of this species. [ABSTRACT FROM AUTHOR]

The article investigates pasteurellosis in lumpsucker Cyclopterus lumpus that are farmed in Norway. Topics include the use of cleaner fish lumpsucker increasing dramatically in Norwegian and Scottish aquaculture as well as the Norwegian Veterinary Institute diagnosing systemic infection with the Pasteurella single species (sp.) in 16 different aquaculture facilities. Also mentioned are the combined observations from field and laboratory studies supporting the hypothesis on Pasteurella sp.

This study describes a co-infection of Kudoa islandica (Myxozoa) and Nucleospora cyclopteri (Microsporida) in farmed lumpfish, Cyclopterus lumpus L. , in Norway. Several other parasites ( Cryptocotyle sp., protozoan ciliates and Gyrodactylus sp.) were also found in gills. In June 2013, the mortality in a farmed lumpfish population increased to 65%. Lumpfish showed erratic swimming behaviour and loss of weight. At necropsy, nodules in the kidney were the only visible lesions. Histologically, all fish showed severe changes with gill inflammation and necrosis in the spleen, kidney and liver. Haemorrhages and necrosis were observed in some hearts. Intracellular microsporidians associated with the lesions were detected in most organs using histological examination and Calcofluor White. Kudoa spores were diagnosed in the skeletal muscle, but no inflammatory response was associated with the presence of the plasmodia. Comparison of 18S ribosomal DNA sequences showed 100% similarity to Kudoa islandica and Nucleospora cyclopteri. Kudoa islandica and N. cyclopteri have previously been described associated with lesions in wild lumpfish in Iceland. In the present case, N. cyclopteri is believed to be the main cause of systemic pathology. This is the first description of K. islandica and N. cyclopteri causing pathology in farmed lumpfish in Norway. [ABSTRACT FROM AUTHOR]

The article offers information on a study which aims at conducting evaluating efficacy of formalin, hydrogen peroxide and salinity in treating lumpfish (Cyclopterus lumpus L.) infected with Gyrodactylus cyclopteri. It mentions that in vitro experiments were conducted to evaluate effectiveness of various doses of formalin, hydrogen peroxide and fresh and brackish water. It states that hydrogen peroxide and brackish water were as effective at controlling G. cyclopteri as maximum dose of formalin.

The sea louse Caligus elongatus utilizes a range of marine fish species as hosts, and it has been suggested that fish farms are infected with adult C. elongatus from wild fish hosts. We assessed experimentally whether dislodged lice return to their original host species. Adult lice from wild lumpfish and saithe were presented to lumpfish, sea trout, Atlantic cod, saithe and European plaice. All fish species became infected. Lumpfish and cod were strongly preferred, followed by saithe, trout and plaice. Lice from wild saithe showed a preference for saithe and lumpfish, followed by cod, sea trout and plaice. The mtCO1 gene was used to determine the genotypes of the lice. Lice from lumpfish were genotype 1. Lice from saithe were mainly genotype 2. The two genotypes of C. elongatus differed slightly in their host preferences: lice from saithe were less discriminating. The data support the hypothesis that adult C. elongatus may transfer between different host species. Cod is an attractive host for lice from both lumpfish and saithe, which suggests that C. elongatus may become a serious pest of farmed cod. [ABSTRACT FROM AUTHOR]