Abstract

Eagle rays (Aetobatus narinari) in managed environments are prone to infestation and secondary consequences from monogenean parasites. Despite intensive quarantine for this species, breakthrough infestations occur with some regularity due to the life cycle, anatomical location the parasites inhabit on the animal, the mucus barrier on the animals, the poor efficacy of typical treatments and bacterial digestion of waterborne treatments. In a large multi-species aquarium, eagle rays were routinely removed and treated with regular immersions of 10 ppm praziquantel for x minutes to manage their parasite loads. The animals were infested by Decacotyle floridana, a genus-specific monocotylid monegene.^1,2 This technique proved inadequate to eradicate the monogenes and, over time, the immersion time intervals were shortened in order to keep parasite loads reduced. Since whole system treatment was difficult due to size of the enclosure and possible impacts on other species, oral praziquantel (100 mg/kg) was given by gavage to anesthetized rays. This technique was used in Rhinobatos annulatus at 150 mg/kg and found to be safe and effective.³ Five to seven days later, the animals were placed in 10 ppm praziquantel baths for 3 hours to evaluate monogene amounts by a sugar floatation method developed at the facility. Our results demonstrated dramatic decreases but not elimination of the parasites and though most rays tolerated the treatments well, one animal developed aberrant behavior and anorexia after her second treatment series and eventually had to be euthanized. Timing of her morbidity did not coincide tightly with the treatment, but the cause of her demise is still pending full necropsy as well as the evaluation of plasma and CSF praziquantel levels. Through these investigations we hope to determine the maximum required interval for treatment to maintain low numbers of parasites, though eradication is the goal.

Acknowledgements

The authors wish to thank Dr. Leslie Chisholm, South Australian Museum, Adelaide; Lara Croft, SeaWorld, Orlando, FL, USA; the veterinary and husbandry staffs at the Living Seas with Nemo and Friends, Walt Disney World Resorts, with special thanks to Charlene Burns and Amy Reierson.

Literature Cited

1.  Chisholm LA, Whittington ID, Fischer AB. A review of Dendromonocotyle (Monogenea: Monocotylidae) from the skin of stingrays and their control in public aquaria. Folia Parasitologica. 2004;51(2–3):123–130.

2.  Marie AD, Justine JL. Monocotylids (Monogenea: Monopisthocotylea) from Aetobatus cf. narinari off New Caledonia, with a description of Decacotyle elpora n. sp. Systematic Parasitology. 2005;60(3):175–185.

3.  Vaughan DB, Bye S, Senzer J. Working towards optimising oral praziquantel for treating monogenean ectoparasites of captive fishes. In: Proceedings from the International Aquarium Congress, Capetown, South Africa; 2012. Available online: http://iac2012.co.za/images/uploads/David_Vaughan_TEXT_-_Working_towards_optimising_oral_praziquantel_for_treating_monogenean_ectoparasites_of_captive_fishes.pdf