Management of Multiple Protozoan Ectoparasites in a Research Colony of Axolotls (Ambystoma mexicanum)

Axolotls (Ambystoma mexicanum) from a research colony presented with multifocal, white chalky to gray skin lesions, a diffuse whitish to blue hue to the integument, and friable gill filaments. Skin scrapings and wet mounts revealed Chilodonella, Ichthyobodo, and a trichodinid species. The average overall burden (that is, all 3 species) per axolotl ranged from 0 to 25 parasites per 40 × field (p40f; mean ± 1 SD, 2.6 ± 5.5), with a prevalence of 12%, 60%, and 48%, respectively. Concurrent with husbandry modifications, axolotls were treated with an 8-h static immersion bath that contained 0.025 mL/L 37% formaldehyde. Chilodonella organisms were no longer observed after the initial treatment, and Ichthyobodo decreased from 2.4 ± 5.6 to 0.6 ± 1.8 organisms p40f. However, the average overall burden increased 4-fold to 10.5 ± 9.8 parasites p40f, and the trichodinid organisms increased 13-fold from 0.8 ± 2.3 to 10.4 ± 9.2 organisms p40f. A second treatment consisted of an 8-h immersion bath that contained 0.05 mL/L 37% formaldehyde on 2 consecutive days. A significant change was noted in the average overall burden of 0.5 ± 1.1 parasites p40f, a greater than 5- and 21-fold decrease from pretreatment and after the initial treatment, respectively. No significant change between the first and second treatment was observed for Ichthyobodo, with 0.6 ± 1.2 organisms p40f, but this number represented a significant decrease from pretreatment. After the second treatment, the trichodinid organism was detected in only one axolotl, with a low overall burden of 0.2 ± 0.4 organisms p40f and resulting in a significant decrease in the trichodinid count to 0.01 ± 0.04 organisms p40f. Treatment with formalin (37% formaldehyde), in conjunction with husbandry improvements, was effective in significantly reducing ectoparasite burden and eliminating clinical symptoms in axolotls but did not fully eliminate all protozoa.