Channel catfish were fed a sinking diet containing 3% oxytetracycline
(OTC) once-a-day (SID) or twice-a-day (BID) for 2 and 3 weeks and live
r and muscle residues were determined. HPLC analysis for muscle indica
ted mean OTC levels of 0.052 ppm (0-0.15) for control, 0.242 ppm (0-2.
95) for SID, and 0.979 ppm (0-11.0) for BID-dosed fish. Liver was 0.00
3 ppm (0-0.08) for control, 0.188 ppm (0-0.52) for SID, and 1.022 ppm
(0-9.3) for BID-dosed fish. The Charm II assay detected OTC (control p
oint set at 100 ppb) in 6.9% of muscle and 10.0% of liver in controls,
47.4% of muscle and 56.0% of liver in the SID group, and 78.0% of mus
cle and 80.0% of liver in the BID group. An interfering peak on HPLC w
as detected in 24.0% of the muscle samples of controls, but not livers
, which affects this assessment. Liver false negative rate was 29.0% a
nd false positive rate was 13.0%, and setting the optimal control poin
t changed the false positive rate to 12.9%. A positive correlation (0.
946) for muscle and liver OTC levels was calculated, indicating liver
may be a suitable alternative to muscle for screening OTC in channel c
atfish. The CITE PROBE Tetracycline test kit failed to reliably detect
OTC in catfish muscle homogenates.