Pathological findings in captive syngnathids: Pipefish, seadragons and seahorses

Syngnathids are teleost fishes that include seahorses, pipefishes, and seadragons, which are commonly displayed in public aquariums. There is limited bibliographic information available regarding the diseases affecting these species. A retrospective pathological study was conducted on 392 syngnathids: 274 seahorses, 92 pipefishes, and 26 seadragons from various aquaria. All individuals underwent necropsy and histopathology, with molecular (n = 63) and parasitological (n = 45) analyses conducted on selected cases. The identified pathologies were classified as either infectious or environmental based on their etiology. Among the infectious agents, non-mycobacterial bacteria were the most prevalent (15.1 %), followed by mycobacteria (6.1 %). Parasites represented the second most relevant group, ciliated protists (10.2 %) were most common; of which scuticociliates were most the frequently observed. Trematodes were detected in 6.1 % of cases, while cestodes and nematodes were each identified in 0.24 % of individuals. In addition, two species of myxozoans, as well as Sphaeromyxa sp., were identified (2.7 %). Lastly, phaeohyphomycosis was observed in 1.46 % of the specimens. Within the environmental category, the most frequent pathology was bilateral symmetrical myopathy (34.1 %), followed by gas bubble disease (4.63 %). No neoplastic or congenital diseases were observed. This study stands out for the large number and diversity of species analyzed, significantly advancing our understanding of pathology in this group of fishes. Several etiological agents not previously reported in syngnathids were observed for the first time (morphology compatible with C. longicollis, Sphaeromyxa sp., Trypanorhyncha gen. sp., among others).