Florfenicol residue depletion in channel catfish, Ictalurus punctatus (Rafinesque)

Florfenicol is a broad-spectrum antibiotic currently used in salmon aquaculture and proposed for use in channel catfish. A residue depletion study was performed under commercial aquaculture conditions to determine a withdrawal period. Market weight catfish (∼ 2 lb) maintained in a 0.1 acre test pond at a 7000 fish/acre stocking density were dosed with commercially formulated florfenicol in feed for 12 days at an average rate of 9.3 mg/kg b.w./day over the last 10 days, or 93% of the proposed dose. Twenty fish each were collected 1, 2, 4, 7, 14, and 21 days post withdrawal of medicated feed and levels of the marker residue, florfenicol amine (FFA), in muscle tissue were determined via a validated HPLC-UV method. By 4 days average muscle FFA levels were below the proposed 1000 ppb tolerance for FFA and beyond this time point all individual fish were below this level.