Clinical and Pathological Findings Associated with Mycobacteriosis in Captive Syngnathids

SIMPLE SUMMARY: Syngnathids are teleost fish that include seahorses (Hippocampus ssp.), pipefishes (Syngnathus spp.), common seadragons (Phyllopteryx taeniolatus) and leafy seadragons (Phycodurus eques). Some species are currently threatened. Reproduction and maintenance in aquariaare complicated and highly contagious diseases, such as mycobacteriosis, can trigger numerous casualties. The most frequently common species observed in fish are Mycobacterium marinum, M. fortuitum and M. chelonae, which belong to the group of non-tuberculous mycobacteria. Stress factors, poor water quality, bad management and high population densities are associated with a higher prevalence of this disease. This study describes the clinical signs and granulomatous lesions associated with mycobacteriosis in syngnathids. M. fortuitum and Mycobacterium spp. were isolated in 4 and 14 syngnathids, respectively. Seven samples were positive against M. chelonae and M. marinum common primers. Considering the scarcity of pathological studies in syngnathids, these findings can help to improve the clinical management and survival of these animals in captivity. ABSTRACT: 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.