Florfenicol in Fish: Uses, In-Feed Dosing and Withdrawal
Florfenicol is an FDA-approved amphenicol antibiotic for fish, given in medicated feed against bacterial diseases such as enteric septicemia of catfish, with sourced dose and a 15-day withdrawal.
Overview
Florfenicol is a broad-spectrum antibiotic of the amphenicol class, a fluorinated synthetic analog of thiamphenicol. It inhibits bacterial protein synthesis by binding the 50S ribosomal subunit. In aquaculture it is the active ingredient of the FDA-approved medicated feed Aquaflor (a Type A medicated article containing 500 g florfenicol per kg) and is given by mouth in feed. In the United States it is dispensed only under a Veterinary Feed Directive (VFD).
What it treats
Florfenicol is used against gram-negative and some other bacterial diseases of fish. Approved indications include enteric septicemia of catfish associated with Edwardsiella ictaluri, columnaris disease associated with Flavobacterium columnare in freshwater-reared finfish, coldwater disease associated with Flavobacterium psychrophilum in freshwater-reared salmonids, furunculosis associated with Aeromonas salmonicida in freshwater-reared salmonids, and streptococcal septicemia in freshwater-reared warmwater finfish.
Administration and dosing
Florfenicol is administered in medicated feed (oral route). The following figures are from the FDA approval and the Merck Veterinary Manual. Treatment must follow a confirmed bacterial diagnosis and a valid VFD.
| Item | Value | Source |
|---|---|---|
| Route | Oral, in medicated feed (Aquaflor) | FDA |
| Dose, coldwater disease in salmonids | 10 mg florfenicol/kg fish/day for 10 consecutive days | FDA (NADA 141-246) |
| Approved dose range, freshwater-reared finfish | 10 to 15 mg/kg fish/day, not exceeding 10 days | FDA label |
| Withdrawal period | 15 days | Merck Veterinary Manual / FDA |
| Dispensing | Veterinary Feed Directive (VFD); VFD expiry not over 15 days | FDA |
Doses are calculated on fish body weight, so an accurate biomass estimate and good feed acceptance are important; sick fish that stop feeding may not receive an effective dose, which is one reason early diagnosis matters.
Resistance and stewardship
As with all antibiotics, overuse or incorrect use of florfenicol selects for resistant bacteria, which can spread within and beyond the farm. Florfenicol should be reserved for diagnosed bacterial disease, used at the labeled dose for the full course, and combined with husbandry, biosecurity and vaccination to reduce the underlying need for antibiotics.
Regulatory status and withdrawal
Florfenicol (Aquaflor) is FDA-approved for the listed indications, dispensed under a VFD, with a 15-day withdrawal period before harvest of food fish. Legal status, approved species, dose and withdrawal rules vary by country and apply to food fish; consult a fish-health veterinarian and the current label before use.