Abstract

Electric eels present unique veterinary challenges. These electric fish, which are gymnotiform knifefish and not true eels, are native to the murky freshwater of the Orinoco and Amazon basins in South America.^1,2 They are obligate mouth breathers possessing highly vascular and diverticulated oral mucosa adapted for respiration with the skin and rudimentary gills functioning mostly for carbon dioxide elimination.³ Electric eels can reach lengths exceeding 2.5 meters and have specialized electric organs capable of discharging low-amperage bursts of electricity that can exceed 600 volts depending upon the length of the fish.^4,5 Special handling protocols and equipment must be used to preserve patient and staff safety, including thick, rubberized gloves and nonconductive transport containers, nets, and restraint devices.⁶ Anesthesia has been used in our practice to facilitate diagnosis and treatment of a subcutaneous pneumocyst, gastric foreign body, and neoplasia. Anesthesia involved forced immersion in high concentration, buffered MS-222 (250–300 ppm) in oxygenated water and maintenance out of water at lower concentrations (100–150 ppm) with mechanical gill ventilation, oral oxygen supplementation and temperature regulation. Monitoring anesthetic depth included use of a speaker-enabled voltmeter to produce audible clicks whenever electric pulses were emitted.⁵ During induction, strong electric pulses ceased before the weaker background sensory pulses (about 10 V) and both ceased when the eel was fully anesthetized allowing for safe handling. Diagnostics included imaging (radiography, ultrasound and MRI), bloodwork and tissue biopsy for histopathology. Treatment for primitive neurectodermal tumors has been attempted with conventional and laser surgery and, most recently, concurrent chemotherapy.

Acknowledgements

The authors want to acknowledge and sincerely thank the talented staff of the Animal Health and Fishes Departments at Shedd Aquarium for their dedication to the highest standards of animal care and welfare. Special thanks are extended to the veterinary technicians and former vet tech William Hana for their ingenuity in development of equipment used specifically for electric eel anesthesia and handling.

* Presenting author

Literature Cited

1.  Binohlan CB, Reyes RB. Electrophorus electricus (Linnaeus, 1766): electric eel. Fishbase [Internet]. Version 12/2013 [cited 31 Jan 2014]. Available from: www.fishbase.org/summary/Electrophorus-electricus.html. 2013.

2.  IUCN [Internet]. Electrophorus electricus. IUCN Red List of Threatened Species. Version 2013.2 [cited 31 Jan 2014]. Available from: www.iucnredlist.org/details/167700/0. 2013.

3.  Johansen K, Lenfant C, Schmidt-Nielsen K, Petersen JA. Gas exchange and control of breathing in the electric eel, Electrophorus electricus. Z Vergl Physiol. 1968;61:137–163.

4.  Moyle PB, Cech JJ. Fishes: An Introduction to Ichthyology. 2nd ed. Englewood Cliffs, NJ: Prentice Hall; 1988: 253–254.

5.  Bennett MVL. Electric organs. In: Hoar WS, Randall DJ, eds. Fish Physiology. Vol 5. New York, NY: Academic Press; 1971: 380–391.

6.  Poll CP, Hana WC, Homeier BN, Van Bonn WG. Two shocking cases: anesthesia and surgery of the electric eel, Electrophorus electricus. In: Proceedings from the 33rd Eastern Fish Health Workshop, Atlantic Beach, NC; March 31–April 4, 2008: p. 70.