Experimental induction of mouthrot in Atlantic salmon smolts using Tenacibaculum maritimum from Western Canada.

Mouthrot, or bacterial stomatitis, is a disease which mainly affects farmed Atlantic salmon, (Salmo salar, L.), smolts recently transferred into salt water in both British Columbia (BC), Canada, and Washington State, USA. It is a significant fish welfare issue which results in economic losses due to mortality and antibiotic treatments. The associated pathogen is Tenacibaculum maritimum, a bacterium which causes significant losses in many species of farmed fish worldwide. This bacterium has not been proven to be the causative agent of mouthrot in BC despite being isolated from affected Atlantic salmon. In this study, challenge experiments were performed to determine whether mouthrot could be induced with T. maritimum isolates collected from outbreaks in Western Canada and to attempt to develop a bath challenge model. A secondary objective was to use this model to test inactivated whole-cell vaccines for T. maritimum in Atlantic salmon smolts. This study shows that T. maritimum is the causative agent of mouthrot and that the bacteria can readily transfer horizontally within the population. Although the whole-cell oil-adjuvanted vaccines produced an antibody response that was partially cross-reactive with several of the T. maritimum isolates, the vaccines did not protect the fish under the study's conditions.

Presence of selected pathogens on the gills of five wrasse species in western Norway.

The objective of this study was to identify gill pathogens in Labridae (wrasse) species used as cleaner fish to control salmon louse in western Norwegian aquaculture. Wrasse are often moved over long distances, raising issues of fish health, welfare and pathogen transmission. Histological examination and real-time RT-PCR analysis of the gills from Centrolabrus exoletus, Ctenolabrus rupestris, Labrus bergylta, L. mixtus and Symphodus melops revealed several pathogens: a new species of Ichthyobodo, Paramoeba perurans, microsporidia, trichodinids, Hatschekia spp., Candidatus Similichlamydia labri and 2 putative new species of Chlamydiae. Cand. S. labri or closely related bacteria were present on most wrasse specimens. Epitheliocysts on the gills of L. mixtus contained large inclusions (120 µm) with actiniae radiating from the inclusion membrane. A possible member of the Candidatus family Parilichlamydiaceae was present at a high prevalence on the gills of L. mixtus, L. bergylta and C. rupestris. Sequencing the 16S rRNA gene showed 93.9% similarity to Cand. S. labri and 96.8% similarity to Cand. Parilichlamydia carangidicola from the gills of Seriola lalandi. This bacterium probably represents a new species within the order Chlamydiales, family Cand. Parilichlamydiaceae. The other Chlamydiae detected on gills of S. melops could represent a new species in Cand. genus Syngnamydia. Ichthyobodo sp. and Paranucleospora theridion were detected on the gills of nearly all individuals, while Paramoeba spp. were detected on the gills of L. bergylta and L. mixtus. Trichodinids, microsporidia and parasitic copepods had low prevalence. Viral haemorrhagic septicaemia virus was not detected.

Genotyping of Tenacibaculum maritimum isolates from farmed Atlantic salmon in Western Canada.

Mouthrot infections (bacterial stomatitis) have a significant impact on the Atlantic salmon aquaculture industry in Western Canada due to economic losses and fish welfare. Bacteria isolated from lesions in the field have been identified as Tenacibaculum maritimum. Mouthrot is different to classical tenacibaculosis, which is most commonly associated with ulcerative lesions, frayed fins and tail rot. The marine fish pathogen T. maritimum is found worldwide; however, in Western Canada, the knowledge of the genetic profile of T. maritimum is limited. This study looked at increasing this knowledge by genotyping T. maritimum isolates collected from Atlantic salmon from farms in Western Canada. These genotypes were compared to other species of the genus Tenacibaculum, as well as other known sequence types within the species. The Western Canadian isolates belong to two new sequence types within the T. maritimum species. Phylogenetic analysis shows that the isolates form a distinct branch together with T. maritimum NCIMB 2154T separate from other Tenacibaculum type strains, and they are most closely related to strains from Norway and Chile.

Genetic variation among Flavobacterium psychrophilum isolates from wild and farmed salmonids in Norway and Chile.

AIMS: To aim of the study was to describe the genetic relationship between isolates of Flavobacterium psychrophilum with a main emphasis of samples from Chile and Norway. The isolates have been obtained from farmed salmonids in Norway and Chile, and from wild salmonids in Norway, but isolates from North America and European countries are also included in the analysis. METHODS AND RESULTS: The study is based on phylogenetic analysis of 16S rRNA and seven housekeeping genes (HG), gyrB, atpA, dnaK, trpB, fumC, murG and tuf, and the use of a multilocus sequence typing (MLST) system, based on nucleotide polymorphism in the HG, as an alternative to the phylogenies. The variation within the selected genes was limited, and the phylogenetic analysis gave little resolution between the isolates. The MLST gave a much better resolution resulting in 53 sequence types where the same sequences types could be found in Chile, North America and European countries, and in different host species. CONCLUSIONS: Multilocus sequence typing give a relatively good separation of different isolates of Fl. psychrophilum and show that there are no distinct geographical or host-specific isolates in the studied material from Chile, North America and Europe. Nor was it possible to separate between isolates from ulcers and systemic infections vs isolates from the surface of healthy salmonids. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows a wide geographical distribution of Fl. psychrophilum, indicating that the bacterium has a large potential for transmission over long distances, and between different salmonid hosts species. This knowledge will be important for future management of salmonids diseases connected to Fl. psychrophilum.

Francisella halioticida sp. nov., a pathogen of farmed giant abalone (Haliotis gigantea) in Japan.

AIMS: In 2005, a Francisella sp. was isolated from diseased cultured giant abalone (Haliotis gigantea) in Japan. The aim of this study was to clarify the taxonomic status of this Francisella sp. Shimane-1 isolate in relation to the four described Francisella species. METHODS AND RESULTS: The 16S rRNA gene and several housekeeping genes of the Shimane-1 were compared to isolates of the four recognized species within the Francisella genus. DNA-DNA hybridization (DDH) and biochemical profile comparison were performed with the two phylogenetically closely related species, Francisella philomiragia and Francisella noatunensis. Results show that the Shimane-1 is genetically different from all described Francisella species and differs phenotypically from F. philomiragia and F. noatunensis. The average DDH similarity of Francisella sp. Shimane-1 to F. noatunensis ssp. noatunensis (NCIMB14265(T)) and to F. philomiragia (DSM7535(T)) was 49·2 and 61%, respectably, clearly supporting the establishment of Shimane-1 as a new species within the Francisella genus. CONCLUSIONS: The phenotypic and genetic results presented in this study suggest the establishment of Shimane-1 as a novel species, for which the name Francisella halioticida sp. nov. (=LMG26062(T), =DSM23729(T)) is proposed. SIGNIFICANCE AND IMPACT OF THE STUDY: This study clarifies the taxonomic position and characteristics of a novel mollusc pathogenic Francisella species.