A chambered nautilus, Nautilus pompilius, housed in a closed system display tank (80 gallons, ~60° C) at The Florida Aquarium was observed to have a rostral mass protruding from between the tentacles, ventral to the hood. The animal did not evade capture, nor did it struggle during physical examination. The presence of "black shell syndrome"2 was noted.
The mass was flaccid, approximately 4.5 centimeters in diameter and located ventral to the mouth and dorsal to the hyponome, the main organ of locomotion. An aspirate was taken which initially produced three milliliters of blue-tinged fluid, presumably due to pigmentation from hemocyanin, followed by thick, mucopurulent discharge. Based on the condition of the animal and the nature of the discharge, euthanasia was elected, using an overdose of tricaine methanesulfonate (MS-222, FinquelTM).
Utilizing aseptic techniques, we obtained material from within the mass for culture and cytology. Gram, Diff Quick and acid-fast stains were performed for cytology. Total protein of the blue-tinged fluid was obtained with a clinical refractometer. A full necropsy was performed. Tissue samples were obtained for histopathology. Sections were routinely prepared and stained with hematoxylin and eosin. Kinyoun's acid fast staining procedure was performed on the cytology and histopathology slides.
The mass and black discoloration and deformation of the shell were the only gross lesions observed. The total protein of the aspirated fluid was 3.5 g/dl. Gram and Diff Quick stains were unremarkable. Abundant acid-fast rods were identified on cytology. Bacterial culture was positive for Bacillus spp., Actinobacter spp., and Mycobacterium spp. Histopathology of the mass and surrounding tissue revealed an attenuated multifocally eroded to ulcerated epithelium. The tissues were intensely infiltrated by hemocytes containing cytoplasmic eosinophilic granules and fewer agranular hemocytes. Within a cavitary space were moderately sized clusters of degenerate hemocytes and cellular debris. Acid-fast organisms were not identified within histopathology sections.
A nautilus from the same system was found dead two weeks prior to this case. A necropsy was not performed, but the specimen was frozen. According to Ross et al.1 freezing does not kill Mycobacterium spp. in carcasses therefore, following positive identification of the acid-fast bacteria in the euthanized nautilus, the first carcass was thawed in a refrigerator over a three-day period. Utilizing aseptic techniques, fluid and mucous samples were obtained from within the shell, mouth and hemocele for cytology and culture. The presence of acid-fast organisms could not be documented. Shell discoloration and deformation were the only gross lesions observed.
Mycobacteriosis has not been reported in any genera of cephalopods. In this instance, we speculate that the cause of the abscess might have been related to trauma induced by bones, spines or shell from the diet of shrimp, smelt and silverside, or the result of tank mate interaction and aggression. Mycobacteria are ubiquitous organisms in the marine environment. Infections in captive aquatic animals are usually related to reduced immunocompetence induced by captive environmental conditions. Shell disease in this animal might have contributed to reduced immunocompetence due to secondary invasion of parasites and microorganisms.
The authors wish to acknowledge Marj Awai, General Curator, The Florida Aquarium; Eric Hovland, Senior Biologist, The Florida Aquarium; Susan Root, Certified Veterinary Technician, The Florida Aquarium; and Peggy Reed, All Florida Vet Lab.
1. Ross AJ, BJ Earp, JW Wood. 1959. Mycobacterial infections in adult salmon and steelhead trout returning to the Columbia River basin and other areas in 1957. United States Fish and Wildlife Service, Special Scientific Report on Fisheries 332: 34.
2. Sherrill J, C Reidel, J Raymond, M Holland, N Landman, R Montali. 2002. Characterization of "black shell syndrome" in captive chambered nautilus (Nautilus pompilius) at the Smithsonian National Zoological Park. Proceedings for the American Association of Zoological Veterinarians, pp. 337-338.