Ocular pathology in aquarium fish with a focus on the Syngnathidae and Apogonidae families

This study catalogued ocular pathology in fish histopathology submissions to a specialist diagnostic service and investigated associations with species and systemic disease, with a focus on species of conservation interest. Cross-tabulations and Fisher's exact tests were used to identify associations among the variables and results are reported as prevalence ratios (PRs) with 95% confidence intervals (CI). Of 12,488 reports reviewed, ocular histology examination was available for 4,572 submissions, in which histopathological ocular lesions were identified in 18% (813/4572). Most diagnoses (701/813; 87%) were in marine fish. Inflammatory conditions were most common (608/813; 75%), with identification of a bacterial aetiology in 42% (255/608) and a parasitic aetiology in 30% (183/608). Most bacterial infections were due to mycobacteriosis (153/255; 60%) and most parasitic infections were due to scuticociliatosis (114/184; 62%). The Syngnathidae, Centriscidae and Cichlidae families were each more likely than all other families combined to be diagnosed with ocular manifestations of mycobacteriosis (PRs = 2.6, 4.4 and 2.9, respectively, P <0.0001 for each). The Syngnathidae were also more likely to be diagnosed with ocular scuticociliatosis (PR = 1.9, P <0.0001). Fifty-four percent (39/72) of ocular mycobacteriosis and 38% (9/24) of gas bubble disease cases affected threatened or near threatened Syngnathidae species. The Apogonidae were more likely than any other family to have ocular iridovirus (PR = 10.3, 95% CI = 5.5-19.4, P <0.0001) and neoplasia (PR = 8.2, 95% CI = 4.2-16.3, P <0.0001). The endangered Banggai cardinalfish (Pterapogon kauderni) accounted for 13/15 ocular iridovirus and 16/18 mycobacteriosis cases in this family. All cases of neoplasia in the Apogonidae occurred in pajama cardinalfish (Sphaeramia nematoptera). These results should inform clinical diagnosis of ocular disease in aquarium fish and influence training for aquarists, highlighting ocular pathology as a potential early warning of systemic disease. The findings also have direct/indirect consequences for the welfare and conservation of some of these popular flagship fish species.

Clinical and Pathological Findings Associated with Mycobacteriosis in Captive Syngnathids

Mycobacteriosis is an important disease that affects captive and wild aquatic fish. Syngnathids are susceptible to infection by non-tuberculous mycobacteria. The aim of this study was to describe clinical signs, and macroscopic and histological lesions in 25 syngnathids and the molecular characterization of the causative mycobacteria. Clinical presentation ranged from sudden death to non-specific signs, including anorexia, poor body condition, weight loss and marked dyspnea with increased respiratory effort and rate. Gross lesions were mostly ulcers on the tail and small white nodules in the liver, coelomic cavity and inside the eye. The most affected organs were gills, liver, intestine and coelomic mesentery. Microscopic lesions consisted of areas of multifocal to diffuse granulomatous inflammation and bacterial emboli with numerous intralesional acid-fast bacilli. Epithelioid cells, multinucleated giant cells, lymphocytes and fibrous connective tissue, which are commonly observed in granulomatous inflammation, were not observed here. In the real-time PCR, M. fortuitum, M. chelonae and M. marinum common primers, Mycobacterium spp. were detected in 4, 7 and 14 individuals, respectively. In addition, this is the first description of mycobacteriosis found in Syngnathus acus.

Retrospective study of phaeohyphomycosis in aquarium-housed fish, with first descriptions of Exophiala lecanii-corni and Neodevriesia cladophorae in fish

A broadening fish host range is affected by novel and known pigmented fungal pathogens. A review of 2,250 piscine submissions received by the Aquatic Pathology Service, University of Georgia, revealed 47 phaeohyphomycosis cases (2.1%), representing 34 bony and cartilaginous fish species. The majority involved bony fish (45/47, 95.7%) and were predominantly marine (41/47, 87.2%), with only a few freshwater species (4/47, 8.5%). Cartilaginous fish cases included two zebra sharks (Stegostoma fasciatum) (2/47, 4.3%). Northern seahorses (Hippocampus erectus) had the highest incidence overall (7/47, 14.9%). Culture and sequencing of the internal-transcribed spacer region of the rDNA (ITS), large ribosomal subunit gene D1/D2 domains (LSU) and the DNA polymerase II gene (RPB2) were performed for fungal identification when fresh tissue was obtainable. Exophiala, Ochroconis and Neodevriesia spp. were identified, with Exophiala as the most common fungal genus (8/11, 72.7%). Exophiala lecanii-corni and Neodevriesia cladophorae were described for the first time from fish. Microscopically, lesions were characterized by necrosis, granulomatous inflammation and angioinvasion most frequently affecting the skin/fin, skeletal muscle and kidneys. In this study of diverse aquarium-housed fish species, phaeohyphomycosis cases occurred sporadically and in rare outbreaks with variable pathologic presentations, tissue distributions and severities.

Systemic phaeohyphomycosis in splitnose rockfish (Sebastes diploproa) caused by Devriesia sp

A novel pathogen was documented after two wild-caught, juvenile, splitnose rockfish presented with buphthalmia, grey corneal endothelial plaques and evidence of uveitis. Cytologic evaluation of ocular contents revealed fungal hyphae. Histologic evaluation identified multiple fungal granulomas and granulomatous inflammation in the globes, periocular tissue and heart. Fungi were slender, hyphenated and branched at angles, had parallel cell walls and had brown pigmentation in haematoxylin- and eosin-stained sections. Both fish were diagnosed with phaeohyphomycosis. Culture with nuclear ribosomal RNA internal transcribed spacer (ITS) segment identification further classified the fungus as Devriesia sp., which has not been previously documented as a cause of disease in animals.

A CLUSTER OF CASES OF THYROID HYPERPLASIA IN AQUARIUM-HOUSED TROPICAL MARINE TELEOSTS FOLLOWING A CHANGE OF SALT MIX BRAND

Follicular thyroid hyperplasia was diagnosed in nine out of 32 (28%) marine tropical teleosts housed in a public aquarium over a 9.5-mo period. These proliferative lesions were considered to be the cause of death in five of these fish. Iodine concentration was undetectable in nonozonized water (<0.005 mg/L), suggesting that an environmental iodine deficiency was the cause of these hyperplastic thyroid lesions. The only significant modification in the husbandry was a change, 18 mo before the first case, of the commercial salt mix brand used to make artificial seawater. The iodine content in this replacement salt mix was five times lower than that of the salt mix used before. This case series suggests that the iodine concentration in this new salt mix was insufficient to maintain thyroid homeostasis in reef teleosts under the husbandry provided in this institution.

Variation among human, veterinary and environmental Mycobacterium chelonae-abscessus complex isolates observed using core genome phylogenomic analysis, targeted gene comparison, and anti-microbial susceptibility patterns

Mycobacterium chelonae is a member of the Mycobacterium chelonae-abscessus complex and a cause of opportunistic disease in fish, reptiles, birds, and mammals including humans. Isolates in the complex are often difficult to identify and have differing antimicrobial susceptibilities. Thirty-one previously identified rapidly-growing, non-tuberculous Mycobacterium sp. isolates cultured from biofilms, fish, reptiles, mammals, including humans, and three ATCC reference strains were evaluated with nine M. chelonae-abscessus complex whole genome sequences from GenBank by phylogenomic analysis, targeted gene comparisons, and in-vitro antimicrobial susceptibility patterns to assess strain variation among isolates from different sources. Results revealed minimal genetic variation among the M. chelonae strains. However, the core genomic alignment and SNP pattern of the complete 16S rRNA sequence clearly separated the turtle type strain ATCC 35752^T from the clinical isolates and human reference strain “M. chelonae chemovar niacinogenes” ATCC 19237, providing evidence of two distinct subspecies. Concatenation of the partial rpoB (752 bp) and complete hsp65 (1,626 bp) sequence produced the same species/subspecies delineations as the core phylogeny. Partial rpoB and hsp65 sequences identified all the clinical isolates to the appropriate species level when respective cut-offs of 98% and 98.4% identity to the M. chelonae type strain ATCC 35752^T were employed. The human strain, ATCC19237, was the most representative strain for the evaluated human, veterinary, and environmental strains. Additionally, two isolates were identified as Mycobacterium saopaulense, its first identification in a non-fish or non-human host.

Pathologic features of mycobacteriosis in naturally infected Syngnathidae and novel transcriptome assembly in association with disease

Syngnathidae (seahorses, seadragons and pipefish) suffer significant losses from non-tuberculous mycobacteria. However, they produce markedly different lesions in response to the disease compared to other teleost species, notably infrequent granuloma formation. This study evaluated 270 syngnathid fish, from which 92 were diagnosed with mycobacteriosis by histopathology, culture or both. Microscopic lesions variably consisted of random foci of coagulative necrosis in multiple organs, containing high numbers of free bacteria and large aggregates or sheets of macrophages with cytoplasm laden with acid-fast bacilli. Mycobacterial associated granulomas were identified in only six seahorses. Five fish had positive cultures with no observed microscopic changes. RNA-seq of the head kidney was performed to investigate the transcriptome of two infected and six non-infected lined seahorses Hippocampus erectus. Assembled and annotated putative transcripts serve to enrich the database for this species, as well as provide baseline data for understanding the pathogenesis of mycobacteriosis in seahorses. Putative components of the innate immune system (IL-1β, IL-6, TNF, NOS, Toll-like receptor 1, MHC Class I, NF-κβ, transforming growth factor beta, MyD88) were identified in the RNA-seq data set. However, a homolog for a key component in the TH1 adaptive immune response, interferon-gamma, was not identified and may underlie the unique pathologic presentation.

Acute disseminated mycobacteriosis in captive Atlantic guitarfish (Rhinobatos lentiginosus)

An adult female captive-born Atlantic guitarfish ( Rhinobatos lentiginosus) was found acutely moribund on exhibit and died soon after presentation. Abnormalities on autopsy were focal cutaneous erythema on the tail, a small liver, many variably sized friable ovarian follicles, and coelomic effusion. Histologic examination revealed systemic bacterial embolization, and yolk coelomitis with minimal associated inflammation and some mineralization. Bacterial culture of blood and coelomic effusion grew a rapidly growing Mycobacterium species that was further identified as Mycobacterium chelonae by PCR amplification and sequencing of the RNA polymerase subunit beta ( rpoB) gene of isolated genomic DNA. Concurrent reproductive disease may have caused immunosuppression, thus predisposing to the mycobacterial infection. At another institution, an adult male wild-caught Atlantic guitarfish was found dead on exhibit with no premonitory signs. Abnormalities on autopsy were a thin body condition, small liver, and coelomic effusion. Histologic examination revealed acute mycobacterial septicemia. M. chelonae was also identified in this fish by PCR amplification and sequencing. Mycobacteriosis has rarely been reported in captive elasmobranchs. Guitarfish may have greater susceptibility to mycobacteriosis than other elasmobranchs, and acute and chronic manifestations of the disease may exist in this species.

New data on flatfish scuticociliatosis reveal that Miamiensis avidus and Philasterides dicentrarchi are different species

Scuticociliatosis is a severe disease in farmed flatfish. However, the causative agent is not always accurately identified. In this study, we identified two isolates of scuticociliates from an outbreak in cultured fine flounder Paralichthys adspersus. Scuticociliate identification was based on morphological data, examination of life stages and the use of molecular approaches. The isolates were compared with a strain of Philasterides dicentrachi from turbot Scophthalmus maximus and with a strain deposited in the American Type Culture Collection as Miamiensis avidus ATCC® 50180™. The use of morphological, biological and molecular methods enabled us to identify the isolates from the fine flouder as P. dicentrarchi. Comparison of P. dicentrachi isolates and M. avidus revealed some differences in the buccal apparatus. Unlike P. dicentrarchi, M. avidus has a life cycle with three forms: macrostomes (capable of feeding on P. dicentrarchi), microstomes and tomites. Additionally, we found differences in the 18S rRNA and α- and β-tubulin gene sequences, indicating that P. dicentrarchi and M. avidus are different species. We therefore reject the synonymy/conspecificity of the two taxa previously suggested. Finally, we suggest that a combination of morphological, biological, molecular (by multigene analysis) and serological techniques could improve the identification of scuticociliates parasites in fish.