Tenacibaculosis (Tenacibaculum spp)

Physical Signs:

• Skin Ulcers: Deep, necrotic ulcers on the skin often surrounded by a darkened area or zone of yellow. Ulcers often found around the mouth, fins, and body (for pictures see Sandoval )
• Fin Erosion: Fraying and degradation of the fins, especially the caudal (tail) fin.
• Hemorrhages: Reddened areas on the skin and fins due to bleeding.
• Gill lesions: erosion and necrosis with little inflammation, filamentous bacteria mats also found covering the gills and necrotic tissue 6
• Systemic infections can result in some cases, depending on the isolate involved 6
• In cases of Tenacibaculum maritimum yellow mats form on the inside of the mouth especially in Atlantic salmon 7 in some cases teeth can fall out 6

Behavioral Changes:

• Lethargy: Reduced activity and slow swimming.
• Loss of Appetite: Decreased feeding behavior and significant weight loss 8
• Abnormal Swimming Patterns: Fish may swim erratically or show signs of distress due to pain from ulcers.

Causative Agents: 

• T. maritimum_ is one of the better researched species in the genus. It is also known as "yellow mouth disease" (in British Columbia, Canada and Washington State), “gliding bacterial diseases of sea fish”, "marine flexibacteriosis", “eroded mouth syndrome” and “black patch necrosis”. Originally described in 1970s with mortalities among farmed red (Pagrus major) and blackhead (Acanthopagrus schlegelii) seabream in Japan 3. It has strong adhesion to fish skin and mucus, needs seawater (≥10%), optimal growth 25-30°C, gram negative and is thin and rod-shaped 3
• T.soleae* identified from Senegalese sole (Solea senegalensis) and turbot Scophthalmus maximus. Mainly sole specific and causes similar ulcers as other Tenacibaculum species 12
• T. discolor identified from European and Asian sea bass (Dicentrarchus labrax and Lates calcarifer) 12. Less pathogenic/emerging compared to the main species and mainly environmental or opportunistic 3
• T. dicentrarchi identified from Atlantic salmon (Salmo salar) 4 and European sea bass (Dicentrarchus labrax L.) 13. Suggested to be more pathogenic to non-salmonid species [14]
• T. finnmarkense identified from  rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar) 15 16. Is it quite virulent (causes more damage to host, disease at lower doses or spreads/grows faster), but higher doses of the virus are needed to infect at 8 °C than at 4 °C 17. Spilt into 2 genetic sub-groups (called genomovars, gv): gv. finnmarkense and gv. ulcerans 18
• T. ovolyticum identified in Atlantic halibut (Hippoglossus hippoglossus) and farmed Atlantic Salmon (Salmo salar) 19. Grows in cold seawater and associated with deep/cold water environments 20. Mainly an egg pathogen historically, but emerging as a cause of tenacibaculosis in farmed fish 4.

Transmission Methods:

• Direct Contact: 

  • T. maritimum, T. dicentrarchi can be horizontally transferred between fish 17, 21.

• Waterborne:

  • T. finnmarkense: Different strains vary in their ability to cause disease, and the bacterium is not readily transmitted between fish [14]

Environmental Factors: Salinity, water temperature, seasonality, algal or jellyfish blooms can affect susceptibility to Tenacibaculosis 5, 3.

• Some regions: more cases with warming waters (Tasmania); others: winter outbreaks (15–20°C ideal in Spain). 3
• For T. finnmarkense colder water temperatures >8°C increase the risk

Farm Management Practices: Generally high rearing density, excessive feed administration (especially in the case of T.maritimum which focuses in the mouth 6) , fresh to saltwater transfer of smolts (salmonids) and/or mechanical damage of the skin and mucus barrier, healthy fish carrying the disease 3, 23, 5, 3, Some specific risks for other species:

• For T. finnmarkense transferring salmonid smolt from high salinity environments to low sea temps in the sea increases tenacibaculosis infection 17.
• For T. dicentrarchi skin or gill damage increase disease susceptabilty, potentially warmer temperatures 21.
• For T. ovolyticum risks include bad hygiene or presence of disease on eggs, cold deep sea water, possible equipment contamination 21.
• For T. soleae risks include being in Sole/brill aquaculture (Spain), tank systems, high mortality in juveniles

Clinical Examination: Observation of physical symptoms, such as skin ulcers and fin erosion.

Laboratory Tests:

• Bacterial Culture: Isolation and identification of Tenacibaculum spp from tissue samples on selective agar plates with MALDI-TOF MS or biochemical tests identify species 21
• PCR (Polymerase Chain Reaction): Detects bacterial DNA in tissue samples. PCR assays have been developed for T. dicentrarchi, T. maritimum and T. soleae 24 Norway favors MLSA for strain diversity; qPCR is routine in EU labs for surveillance 25, 4
• Histopathology: Microscopic examination of tissue samples to assess the extent of tissue damage and infection, but not for species ID 39

Current Treatments:

• Antibiotics: Most common measure to control T.maritimum with varying degrees of success 3 Administered through medicated feed or water to treat bacterial infections. The bacteria are naturally resistant to quinolones (a type of antibiotics commonly used against gram-negative bacteria), so efficacy is limited 2

Supportive Care:

• Improving Water Quality: Ensuring optimal water conditions to support healing and reduce stress 27
• Reducing Stocking Densities: Reduce stocking density during the whole life cycle to keep stress levels down (low stress = good immunity) and minimise skin damage 27
• Nutritional support: Especially during first feeding, use high quality diets, and functional ingredients (e.g., immunostimulants, certain algae, probiotics or prebiotics) that may enhance skin and gut barriers and reduce lesion severity 27. Essential oils have also shown to reduce mortalities in sea bream 28.

Biosecurity Protocols:

• Regular monitoring of fish health to detect and address (ether by antibiotics or culling) early signs of infection 3
• Different strains of T. maritimum are locally sourced and not internationally, which helps with genetic tracking of outbreaks 1.

Vaccines:

• No commercial vaccine, except for one for turbot in Spain, which needs boosters 31 . The broad genetic variety means broad vaccines fail 3
• Tested vaccines include: barramundi in Singapore, salmon in Tasmania, salmon in Chile 8, whole cell inactivated adjuvanted vaccine against T. finnmarkense [14] and immunization with recombinant proteins against T. finnmarkense 30

Farm Management Practices:

• Using equipment and facilities designed to minimize skin abrasions and injuries.
• Ensuring adequate nutrition to support immune function and wound healing.
• Implementing fallowing periods and site rotations to break the infection cycle 39
• Salmonids that have been exposed to low-strength salinity appear to have a better ability to respond to an infection. 17
• Salmonid transfer to sea above  5˚C significantly lowers T. finnmarkense infection rates 18

Notable Outbreaks:

• Japan (1970s): The first identified outbreaks led to significant losses and increased awareness of Tenacibaculosis.

• Norway (2010s): Major outbreaks started gaining attention, although the bacteria had been present since at least the 1980s. 4.

  • In Finnmark (northern Norway) in 2015 mortalities were up to 40% in recently transferred smolt [14]

• Chile (2010s): Severe outbreaks caused substantial economic impact and prompted industry reforms 3 9.

  • 2018–2019: First major reports post-seawater transfer T. dicentrarchi dominant, mortality up to 10% by mid-2019 (rising from 0% in company stats) 32
  • 2020 new hosts: Clinical cases confirmed in rainbow trout and coho salmon farms (first globally for coho) T. dicentrarchi and T. finnmarkense isolated in Los Lagos 32

• Europe (1990s): First European cases in sea bass (Dicentrarchus labrax) cages, spreading from Japan 33. 2009–2010 Spain: Three outbreaks in wedge sole at 20.5°C; T. maritimum isolated from ulcers 3

• Italy/Greece/Turkey (2000s–2010s): Sea bass farms affected, raising aquaculture concerns 33.​

Lessons Learned: The importance of a supported early life then early detection, robust biosecurity, and coordinated response efforts in controlling Tenacibaculosis outbreaks 39.

Tenacibaculosis Incidence in Canada:

• Tenacibaculosis, particuarly T. maritimum is a significant concern in Canada, particularly in British Columbia, where it affects both wild and farmed salmon populations 34, 29. Recurrent. T. finnmarkense and T. dicentrarchi also contribute to outbreaks, particularly in juveniles post-transfer to net-pens 34
• Diagnosed annually since 2003 across BC salmon farms, with 106 farm-level cases from 2002-2018 audits 34

Geographical Spread:

• The disease is prevalent in marine net pen Atlantic salmon farms in British Columbia, with outbreaks also reported in other regions and in the wild 35.

Economic Impact:

• The annual cost associated with Tenacibaculosis outbreaks in British Columbia is estimated to be $1.8 million, with an additional revenue loss of $3.8 million per year 29.
• A single outbreak can cost up to $500,000 CAD 34

Treatment & Management:

• Management practices include the use of antibiotics during outbreaks, though there are concerns about resistance 34
• Recent research efforts focus on developing vaccines to prevent the disease 29, Onda
• In-feed immune boosting agents have been suggested to help 34

Tenacibaculosis Incidence in Chile:

• Severe outbreaks and reoccurence of Tenacibaculosis have been reported in Chile, causing substantial economic impact and prompting industry reforms 14.
• Primarily caused by T. dicentrarchi (most cases), with T. maritimum and T. finnmarkense less common, it ranked as the second leading cause of Atlantic salmon mortality in early 2023 (32.9% of deaths) 36
• Outbreaks peak after seawater transfer (smoltification stress) and at >1 kg body weight, worsened by handling, low oxygen, algal blooms, or co-infections. Previously misdiagnosed as SRS, cases rose from ~0% to 10% of mortalities since 2019 (SERNAPESCA data) 37
• A new species, T. salmonis, was isolated from a 2018 Atlantic salmon gill outbreak 36

Geographical Spread:

• Span the Chilean Patagonia, from Los Lagos Region in the north to Aysén and Magallanes Regions in the south—covering nearly 1,200 km of marine salmon farms. affecting both wild and farmed salmon populations 36

Economic Impact:

• Industry losses are US$700 million annually for bacterial diseases overall, of which Tenacibaculosis is a part of that 38
• Tenacibaculosis has led to significant economic losses in the Chilean aquaculture industry, highlighting the need for effective management and prevention strategies.

Treatment & Management:

• Heavy use of antibiotics (compared to other global companies), primarily florfenicol and oxytetracycline, which raise serious concerns about antimicrobial resistance (AMR) 38.
• Push for vaccines, probiotics, and regulatory reforms like density limits 38
• In response to outbreaks, Chile has implemented improved regulatory oversight and industry-wide restructuring to manage Tenacibaculosis:
  • Enhanced Diagnostics & Surveillance: SERNAPESCA and ADL Diagnostic intensified monitoring since 2019 across Patagonia farms and to distinguish T. dicentrarchi from salmon rickettsial septicaemia (SRS) 37
  • Density & Site Regulations: Reduced max biomass from 8 kg/m³ to 4 kg/m³ in some areas; fallowing periods extended to 45 months; 2025 decrees eliminated overlapping aquaculture zones in national parks (Atacama, Aysén)
  • Programs to reduce antibiotic use: Pincoy project for example, is aimed to reduce the antibiotic use in Chile salmon aquaculture

Tenacibaculosis Incidence in Norway:

• Tenacibaculosis has been present in Norway since the late 1980s and leads to regular ulcerative outbreaks and high mortalities in farmed salmonids 144.
• Significant outbreaks have been reported, with Tenacibaculum finnmarkense being the most commonly isolated bacterium during these events, *T. dicentrarchi*** noted in some post-smolt events 14.
• A study from 2017-2020 confirmed the high diversity of Tenacibaculum strains (66) in Norway, with 95% of the strains isolated being previously unidentified 4.
• Norwegian T. maritimum isolates cause crater disease (“donut” syndrome) in smolts and can be directly transmitted (horizontally) to salmon 17

Geographical Spread:

• Tenacibaculum spp. have been detected along the entire Norwegian coast, from Akershus in the southeast to Finnmark in the north 4. The north is most affected by Tenacibaculosis outbreaks 4.
• Several strains, such as Tenacibaculum dicentrarchi, are present within restricted areas, while others are found across different localities and hosts 17

Economic Impact:

• Tenacibaculosis in 2020 was considered the fifth most important cause of mortality in on-growing salmon in Norway 29.
• The disease causes major economic losses due to increased mortality, reduced quality at harvest, and the need for antibiotic treatments 29.

Treatment & Management:

• Recent efforts include the development of vaccines against Tenacibaculum bacteria 29.
• Keeping smolt for 4 weeks in 26 per mille seawater can significantly reduce the effect of susceptibility to tenacibaculosis after transfer to the sea and they can better respond to an infection 17

• On Chinook salmon (Oncorhynchus tshawytscha) farms, mainly in the Marlborough Sounds since the late 1980s, with increased relevance during summer mortality events from 2012 onward 39, [22]

• Marlborough Sounds main hotspot, with problems of co-infection with New Zealand Rickettsia-like Organism (NZ-RLO) and T. maritimum in Chinook salmon 39
• Akaroa Harbour (Canterbury/South Island): Sporadic detections of NZ-RLO3 (lower pathogenicity), confirmed in targeted surveillance (2015–2017) 39
• Stewart Island (Southland): No detections in surveillance sampling of farmed or wild salmon 39

• As a "priority disease" for NZ King Salmon (the dominant producer), it prompted industry vaccination programs (2022 onward) and MPI biosecurity responses (Controlled Area Notices until 2023), indicating significant operational costs for containment, surveillance, and lost production 39

• MPI Controlled Area Notices (until 2023) restricted stock movements between Marlborough Sounds zones (e.g., Pelorus/Queen Charlotte Sounds) and other sites like Akaroa; emphasis on water quality and temperature control (>17°C exacerbates outbreaks) 39

• In Spain, France, Italy, and Greece, T. maritimum and T. dicentrarchi cause outbreaks in nursery and pre-grower stages, with mortalities exceeding 30% in affected cages or RAS units 8

• Primarily affects sea bass, sea bream, and flatfish (turbot, sole) in Mediterranean countries like Spain, Greece, Italy, France, and Turkey and peaks in warmer months 8

• Considered one of the most important diseases in European Sea bass, in some marine areas or in recirculation systems, they severely threaten production with mortalities rising over 30%. 40

• Antibiotics in medicated feed or as bath treatments, which raises concerns on resistance 3
• Treatment is difficult, and results of how the bacterium responds to a drug can vary alot from lab to field resulting in the disease having a higher overall impact 41

• T. maritimum affects farmed Atlantic salmon, particularly in post-smolt phases, though less dominantly than in Norway or south Europe 3

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• The disease has affected Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), greenback flounder (Rhombosolea tapirina) and striped trumpeter (Latris lineata) 23
• February 2023 there was an outbreak at near Bruny Island, in combination with a Tasmanian Rickettsia-Like organism 42

• Bruny island and Okehampton had an outbreak in February and May, 2023 42

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• 368.5 kilograms of in feed antibiotics, oxytetracycline (OTC), were used to control the 2 outbreaks 42