Abstract
A captive 2-3 year old brook trout, Salvelinus fontinalis, presented to the North Carolina State University, College of Veterinary Medicine Field Service for evaluation of a cranial mass. The fish was housed in an artificial freshwater stream environment at a regional life science museum. A number of coins were noted on the bottom of the aquatic display. The history included the fact that the fish was moderately depressed for several weeks and had a decreased appetite. On physical examination the fish appeared sluggish and had a 1.0 x 1.0 cm raised lesion on the right side of the head, caudal to the eye. The right eye was slightly exophthalmic.
The fish was anesthetized with 150 ppm tricaine methanesulfonate (MS-222) and a biopsy of the raised cranial lesion was taken for histopathology. Biopsy results indicated a nerve sheath tumor, a generic term for tumors derived from Schwann cells. These tumors are characterized by being locally aggressive and rarely metastatic. When possible and practical, they are treated with wide surgical excision.
During the ten days following the anesthesia and biopsy procedure, the trout's condition deteriorated and the curator elected to euthanatize the fish. On necropsy, the significant gross findings included a corneal abrasion of the right eye, pale gills and flesh, and the presence of a corroded 1995 penny in the fish's stomach. A fresh liver sample saved and analyzed for zinc levels showed a concentration of 833 parts per million (ppm) in this tissue. Although there is no "normal" range for zinc levels in this species, one study in rudd (Scardinius erythrophtalmus) reported baseline liver values of about 3.0 ppm.1
All pennies minted from 1983 to the present are composed of 96% zinc and 2.5% copper. This trout apparently consumed a penny, which became lodged in its digestive tract. The penny was exposed to the corrosive acids in the fish's stomach, likely causing the zinc to be leached out into the bloodstream and tissues. Zinc toxicity can manifest as a hemolytic anemia, which was observed in this fish by the pale muscle and gills, and the watery appearance of the fish's cardiac blood. It is our feeling that the fish's general clinical condition was a result of the zinc toxicity and related hemolytic anemia rather than any effects of the nerve sheath tumor. This case is being used by the science center as an educational exhibit to warn the public of the dangers of coin tossing.
Acknowledgements
The authors wish to thank Dr. Robert Bakal and Sherry Samuels for their assistance with this project.
References
1. Van Hoof, F., and M. Van San. 1981. Analysis of copper, zinc, cadmium and chromium in fish tissue; a tool for detecting metal caused fish kills. Chemosphere 10: 1127-1135.