Abstract

This study began as a lead toxicity investigation in largemouth bass (Micropterus salmoides), looking at the implications of fish ingesting lead sinkers (split shots). It is known that waterfowl and other birds consume lead fishing sinkers resulting in detectable blood lead levels and potentially lead toxicity. The idea for this study originated from a clinical case, a sick electric eel (Electrophorus electricus) that had consumed lead aquatic plant sinkers in captivity that presented to the North Carolina State University College of Veterinary Medicine. The lead levels in the eel were measured but there were no base line data to compare these figures and apparently nothing published on lead toxicity from lead sinker consumption in fish. Our study was designed to determine if fish that have lead in their stomach will absorb lead into their bloodstream and at what level and how quickly. Ten fish were placed in individual 57 liter aquariums on a recirculating water system of which 15% was changed weekly. They were fed three times a week and fasted the day before and day of the experimental procedure. Using a heparinized 25 g needle, blood was drawn from eight experimental fish and two control fish from the caudal vein to establish a healthy plasma biochemical base line. A total of 10 fish were used for the lead toxicity study and 11 for the blood reference range; the discrepancy is due to an unscheduled mortality during the blood collection. The fish were anesthetized and maintained with buffered tricaine methanesulfonate (MS-222) at concentrations of 200 ppm and 100 ppm respectively. Commercial lead sinkers of 10 g for every kg of fish were implanted in the stomach using blunt forceps. An endoscope was used to verify the gastric implantation of the split shots. Within 1 hour, one of the fish regurgitated the split shot and the last fish regurgitated its lead shot 3 days after the procedure. Although the lead sinkers were regurgitated, data from the blood was still analyzed to establish blood biochemical parameters for largemouth bass. Since blood biochemical parameters are used as a common health assessment tool, it is essential to have an established reference range. The blood sample was initially stored at -80°C for 10 days and centrifuged. The plasma was isolated and analyzed using a Vetscan analyzer (Abaxis, Avian Reptilian Profile Plus rotor, software version 5.118.2) designed to automatically determine albumin, bile acid, aspartate aminotransferase, creatine kinase, total protein, globulin, glucose, uric acid, calcium, phosphorus, potassium range, and sodium. The plasma values resulted with an albumin range of 1.5-2.4 g/dL , bile acid range of <35-91 µmol/L, aspartate aminotransferase range of 21-115 u/L, creatine kinase range of 334-6493 u/L, total protein 3.5-5.0 g/dL, globulin range of 2-2.8 g/dL, glucose range of 55-106 mg/dl, uric acid range of <0.3-1.3 mg/dL , calcium range of 11.1->16.0 mg/dL, phosphorus range of 7.5-14.2 mg/dL, potassium range of <1.5-1.8 mmol/L, and a sodium range of 147-161 mmol/L. This study determined that largemouth bass are at low risk of lead toxicity from consuming lead shots because of their regurgitation ability. A plasma biochemical reference range for the largemouth bass was also established.