Abstract

A total of seven cases of retinoblastoma-like neoplasms were diagnosed from a group of 48 aquarium-housed striped basses (Morone saxatilis) over a 2-year period, for a prevalence of 15%. Affected fish were wild-born individuals over 10 years of age that have been maintained most of their lives in a 350,000-liter 12°C sea water (30 g/L) indoor closed system. All affected fish showed unilateral exophthalmia/buphthalmia (right eye = 3; left eye = 4) associated with the presence of a large intra-orbital mass often invading the retro-orbital space. Unilateral enucleation with consecutive resection of the tumoral masses was performed on each fish in average 22 days after the clinical signs were first reported (between 0 and 73 days). Histologically, all tumors had characteristic cellular features of retinoblastoma including Flexner-Wintersteiner rosette formations. Post-surgery survival varied from 103 to 325 days (median 219 days). Five of the fish were euthanized due to local regrowth of the tumor, whereas one fish was euthanized due to the development of another retinoblastoma-like tumor in the contralateral eye. The remaining fish is still alive and doing well three months post-enucleation. The cause of this cluster of cases of ocular tumors remains unclear. Nevertheless, the absence of this syndrome in striped basses from the same cohort housed in a different facility in a semiclosed fresh-water system with up to 10% water change per day suggests that environmental factors might play a role in the development of this syndrome.

* Presenting author