Abstract
An essentially species-specific disease was found to be widespread in populations of bicolor damselfish (Pomacentrus partitus) on Florida reefs. Histological examination of affected fish demonstrated that this disease consisted of multiple Schwann cell tumors. The majority of the tumors were neurofibromas and the remainder were classified as malignant schwannomas. Most of the tumors were malignant. Lesions arising in the epidermal and dermal layers were typically hyperpigmented.Populations of P. partitus on 18 of 19 Florida reefs surveyed contained diseased fish. Essentially all (99%) diseased individuals were large, sexually mature fish. Point prevalence values in affected populations ranged from 0.5 to 24% of adult bicolor damselfish. Long term monitoring in the field of fish with tumors indicated that the total duration of the disease from first possible diagnosis to death was 1 to 1.2 years. Significantly higher relative proportions and population densities of the largest size class of P. partitus were found on reefs with a high (greater than 3%) disease prevalence. A comparison of diseased fish, based on a tumor staging system developed for this study, demonstrated that a significantly greater proportion of the affected fish on the high disease reefs were in advanced stages of tumor development. Analysis of small-scale spatial distribution of diseased individuals indicated that these fish were significantly clustered as well as associated with areas of high population density of adult conspecifics.Inoculation of healthy P. partitus with a mixture of whole and lysed tumor cells in the laboratory resulted in tumor development in over 70% of these fish within 5 to 27 months. Fish given similar subcutaneous and intraperitoneal injections of mixed populations of normal cells did not develop tumors.These findings suggest that this disease may be caused by an infectious agent such as an oncogenic virus. The variations in disease prevalence from reef to reef are probably due to differences in population structure, density or adult mortality rates that affect the potential for transmission and expression of these tumors. These population differences may in turn be due to differences in environmental conditions that determine the nature of the habitats available to P. partitus on these reefs.