PLASMA MUSCLE RATIOS OF SULFADIMETHOXINE RESIDUES IN CHANNEL CATFISH (ICTALURUS-PUNCTATUS)

Channel catfish (n = 84) maintained at a water temperature of 27 degre es C were used in a feeding study to determine the plasma to muscle co ncentration ratios of sulfadimethoxine (SDM) and 4-N-acetylsulfadimeth oxine residues. Sulfadimethoxine medicated feed was provided free choi ce at: 42 mg SDM/kg body weight once daily for 5 days and the plasma a nd muscle concentrations of SDM were determined at selected withdrawal times (6, 12, 24, 48, 72, and 96 hours) following the last dose. Cons iderable variation in total SDM tissue concentration among fish within a sampling period was observed. For fish (n = 12) at six hours post-d ose, total SDM concentrations ranged from 1.4-24.8 mu g/mL and 0.6-12. 6 mu g/g, with mean total SDM concentrations of 9.1 mu g/ml, and 5.3 m u g/g for plasma and muscle, respectively. However, a mean plasma:musc le concentration ratio of 1.8:1 +/- 0.3:1 was obtained over all concen trations and sampling periods, The plasma:muscle 95% t distribution in terval for individual fish was 1.2:1 to 2.4:1. A correlation coefficie nt of 0.967 was obtained for the relationship between plasma and muscl e total SDM concentration among individual fish (n = 25), Results of t his study indicate that plasma total SDM concentration may be used to identify samples containing violative SDM muscle residue. No fish cont ained total SDM muscle residues greater than the FDA tolerance (0.1 mu g/g) by 48 hours following the final dose.