Chloramine-T in Fish: Bacterial Gill Disease Dosing and Safety
Chloramine-T is an FDA-approved oxidizing antibacterial for freshwater-reared finfish bacterial gill disease and columnaris, with a label dose, pH-dependent toxicity and a 0-day withdrawal.
Overview
Chloramine-T (sodium p-toluenesulfonchloramide, formula CH3C6H4SO2NClNa) is an organic chlorine compound that acts as an oxidizing antiseptic, releasing active chlorine in water; its aqueous solutions are mildly basic. In aquaculture the FDA-approved product Halamid Aqua (chloramine-T powder for immersion) is used as a waterborne antibacterial applied by bath or flow-through immersion.
What it treats
Halamid Aqua is FDA-approved to control mortality in all freshwater-reared finfish due to bacterial gill disease and due to external columnaris disease (associated with Flavobacterium species, including Flavobacterium columnare). It acts on bacteria on the gills and external surfaces and is not a systemic or internal-disease treatment.
Administration and dosing
Chloramine-T is given by immersion, either as a continuous-flow bath or a static bath. The figures below are from the FDA Halamid Aqua approval.
| Item | Value | Source |
|---|---|---|
| Route | Continuous-flow or static immersion bath | FDA |
| Concentration | Up to 20 mg/L | FDA (Halamid Aqua) |
| Exposure time | As long as 60 minutes | FDA |
| Regimen | On consecutive or alternate days, as many as three times | FDA |
| Withdrawal period | 0 days (none required before harvest) | Merck Veterinary Manual |
The FDA label restricts use to systems that can be flushed: it must not be used in earthen ponds or systems that cannot be flushed after treatment, and in recirculating systems the biofilter is bypassed during treatment and flushing because effects on the biofilter have not been evaluated.
Safety and water chemistry
Acute toxicity of chloramine-T to fish increases as pH decreases, so the same concentration is more toxic in acidic water; the FDA-derived water-quality benchmark is intended to protect aquatic life at pH at or above 6.5. Chloramine-T is also hazardous to aquatic invertebrates and algae, and the undiluted product should not be released into natural waterways. Fish should be observed during treatment and removed if they show distress.
Regulatory status and withdrawal
In the United States Halamid Aqua (chloramine-T) is FDA-approved and sold over the counter for the indications above, with no required withdrawal period before harvest (a 0-day withdrawal). Legal status, approved species and label conditions vary by country and apply to food fish; consult a fish-health veterinarian and the current label before use.