Medical Management of Acute Positive Buoyancy in a Leafy Sea Dragon (Phycodurus eques)
IAAAM 2014
Julie M. Cavin1*; Jeremy F. Brodt1
1New England Aquarium, Boston, MA, USA


An approximately one-year-old leafy sea dragon (Phycodurus eques) presented with acute positive buoyancy 24 days after being placed onto exhibit, and nearly one year after arrival at the New England Aquarium (NEAq). An aggressive appetite and normal behavior were observed on exhibit. Initial physical examination and radiographs revealed an extensive gas viscus in the dorsal coelom, presumed to be a hyperinflated swim bladder. No obvious gastrointestinal obstruction was noted by transillumination. An attempted gastrointestinal radiographic contrast study using barium sulfate was unsuccessful. Treatments during the first four weeks included a carbonic anhydrase inhibitor (acetazolamide 2.5 mg/kg IM q7d x 3 weeks), broad-spectrum antibiotics (enrofloxacin 10 mg/kg IM q4d x 2 weeks and oxolinic acid 1 mg/L continuous immersion x 10 days) for primary bacterial infection or secondary infection due to repeated procedures, and an antifungal (itraconazole 20 mg/kg PO q48h x 2 weeks) based on previous history of sea dragons with Exophiala spp. infection at NEAq. Enteral nutrition was provided as frequently as every other day using crushed frozen mysids or LaFeber's Emeraid® carnivore diet at 1–2% body weight. Percutaneous pneumocystocentesis was performed as necessary to eliminate positive buoyancy. Transient neutral buoyancy and normal orientation occurred following centesis, but positive buoyancy returned within 24 hours.

After one month with no significant change, treatment was altered to manage a possible localized swim bladder and/or systemic acidosis. It was theorized that excess protons, carbon dioxide or lactate from prolonged physiological stress could cause equilibration of concentration gradients between the blood and gas gland rete mirabile prohibiting movement of gases out of the swim bladder.1,2 Sodium bicarbonate (0.5 mg/kg) was administered first intracoelomically diluted in sterile saline (1:1 volume), then intraluminally into the swim bladder in lactated Ringer's solution (0.5 ml) following no change with the intracoelomic infusion. Normal buoyancy and orientation was achieved for six days. A second attempt resulted in a similar transient improvement. After discussion with a colleague regarding treatment of a positively buoyant green moray eel (Gymnothorax funebris), the protocol was altered to administration of enrofloxacin (20 mg/kg) and 6% hetastarch solution (0.5 ml) intraluminally. This treatment was administered three times over 8 days as needed due to recurring positive buoyancy. Voriconazole 20 mg/kg was also administered with the third dose due to a possible fungal nodule observed within the swim bladder. The individual is currently neutrally buoyant at eleven days post final infusion. It is unclear whether the improvement is due to successful treatment of acidosis by sodium bicarbonate, or if the intraluminal fluid is inhibiting recurrence of hyperinflation.

The case is currently ongoing, so the outcome is unknown. However, this case demonstrates that moderately aggressive and diverse treatments can be tolerated by sea dragons.


The authors would like to thank the New England Aquarium Animal Health Department and Fishes Department staff for their assistance in the treatment of this individual. Thank you also to Shane Boylan for his consultations and antibiotic and colloid protocol.

* Presenting author

Literature Cited

1.  Moyle PB, Cech JJ. Fishes. An Introduction to Ichthyology. 3rd ed. Upper Saddle River: Prentice-Hall, Inc.; 1996:590.

2.  Pelster B. pH regulation and swimbladder function in fish. Resp Physiol Neurobi. 2004;144:179–190.


Speaker Information
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Julie M. Cavin
New England Aquarium
Boston, MA, USA

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