Abstract
Seadragons are the largest and perhaps some of the most dramatic-looking teleost fishes encountered in public aquaria. Their rarity, sensitivity, and scrupulous husbandry requirements make them a management challenge, while at the same time they are uniquely susceptible to many factors that are less impactful in other species.1 In general, few causes of morbidity and mortality described in seadragons would be characterized as primary, with chronic stressors and secondary opportunistic disease being most frequently reported, including phaeohyphomycosis, atypical mycobacteriosis, and scuticocilatosis.2-4 Meanwhile, their trophic niche as size-specific ambush predators means that these taxa, unlike many teleosts managed in modern aquaria, often receive live, wild-caught prey items as a significant component of their diet.
A review of several cases involving leafy seadragons from a public aquarium over a 10-year period identified a recurrent incidental finding of digenean parasites associated with the gastrointestinal tract on postmortem examination. While there are relatively few accounts, gastrointestinal parasites of Syngnathidae are reported in the literature.5 These are generally considered incidental findings, though some (such as coccidia in weedy seadragons, Phyllopteryx taeniolatus) are of clinical significance.6 Working with Auburn University’s Fish Parasite and Disease Laboratory, live and preserved samples of the adult parasites and eggs were isolated and diagnosed as a species of the genus Opecoeloides. These were characterized by having a ventral sucker with prominent papillae that is larger than an oral sucker, ceca open via uroproct, and an accessory sucker posterior to the genital pore. Phylogenetic analysis based on the large subunit ribosomal (28S) DNA gene places the parasite among other Opecoeloides spp. Interestingly, the species shares a recent common ancestor (40 nucleotide differences = 96.4% similarity) with Opecoeloides furcatus that infects the stripped red mullet, Mullus surmuletus Linnaeus, 1758.7 In all postmortem exams that identified gastrointestinal parasitism, a separate and definitive cause of death was identified—most commonly disseminated mycobacteriosis. However, egg detection from fecal samples of chronically ill animals frequently displayed significantly elevated egg counts (>20/hpf), when compared with routine surveillance of clinically normal individuals (0–3/hpf). In animals that were treated and cleared of the parasite, reinfection was often seen within several months, supporting ongoing exposure to a source of the digenean parasite’s infective stage—in this instance believed to be wild-caught mysid shrimp, Americamysis bahia. Since this discovery, preventative care for this species was adjusted to include routine quarterly fecal screenings to survey for parasite burden. Elevated egg counts (>5/hpf) were treated with oral praziquantel administered via bioencapsulation, with a goal of reducing overall parasite burden rather than pursuing complete clearance.
Utilization of routine fecal examinations in teleost fish often lags behind management practices for terrestrial animals. A survey of aquatic animal veterinarians who have worked with seadragons found that fecal screening is uncommon in the species, with only 36% of respondents performing this diagnostic during quarantine and only 20% considering it once animals are on exhibit. Overall, gastrointestinal parasites had been diagnosed on postmortem by 60% of respondents and identified nematodes, trematodes, digeneans, and cestodes. Unlike most aquatic animals, Syngnathids produce relatively large and well-formed fecal pellets, and collection of fresh samples is easily accomplished with minimal stress to the animals. This is proposed to be a useful tool in reducing overall physiologic stress and chronic burden on the immune system over the lifetime of the animals and represents an avenue to shift management standards for this taxon toward a more prophylactic approach.
*Presenting author
Literature Cited
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