Inputs · Fish health
Salt (sodium chloride) for fish health
Salt is a cheap, widely used fish treatment, sometimes called the aspirin of aquaculture, for external parasites and handling stress. In aquaponics it belongs in a separate hospital tank, not in the system: the sodium harms plants, and sudden salt changes set back the biofilter.4, 2, 3
Why you need it4, 1, 3
The NCRAC fact sheet says salt, used properly, treats many external parasites, including Costia, Epistylis, Trichodina, Chilodonella and the flukes Dactylogyrus and Gyrodactylus, and relieves stress during handling and transport. FAO says a salt bath helps fish with some external parasites, moulds and bacterial gill contamination, and describes it for white spot. In fish-only recirculating systems, SRAC 452 adds salt because chloride blocks nitrite poisoning (brown blood disease) and because sodium and chloride ease osmotic stress after handling or poor water quality.
How to use it1, 4, 3, 5
Treat in a separate tank. FAO's salt bath: 1 kg of salt per 100 litres of water, fish in it for 20 to 30 minutes, then moved to a second isolation tank at 1 to 2 g of salt per litre for another 5 to 7 days; for a bad white-spot outbreak, all fish may need to come out of the system for at least a week. NCRAC lists dips of 30 seconds to 1 minute in strong solutions, including 3 percent for 15 seconds for brood fish before stocking; prolonged baths at 1 to 3 percent for 30 minutes or until fish show stress; 1,000 to 2,000 ppm in hauling tanks; and 0.1 to 1.0 percent for transport and handling. Measure, do not guess: NCRAC says to know your tank volume, weigh salt on an accurate scale (1 ppm is 0.00378 g per gallon, so 1 percent is 10,000 ppm), try a few fish first, and be ready to move fish to fresh water at the first sign of stress. For nitrite problems in fish-only systems, SRAC 452 gives 6 to 10 parts chloride per part nitrite-nitrogen and SRAC 451 a 10 to 1 ratio; in aquaponics the sources prefer fixing the biofilter and changing water (see gaps).
Cautions2, 1, 3
Keep salt out of the aquaponic system. SRAC 454 says the common practice of adding salt to treat disease or reduce nitrite toxicity is harmful to plant crops, that sodium should stay below 50 mg/L, and that more causes tip burn in lettuce; fish feed already contains some salt. FAO says never to pour the bath water back into the system when returning fish. SRAC 452 says adding salt quickly reduces biofilter efficiency, and the bacteria take 3 to 4 weeks to adjust. FAO adds that any fish medicine should be used only in a hospital tank and never added to the aquaponic unit. Before treating, check ammonia, nitrite, pH and temperature: if many fish are sick, water quality is the likely cause (FAO). Quarantine new fish and never pour hauling water into the system (SRAC 452).
What to buy4
NCRAC says table salt, meat-curing salt, pickling salt and rock salt are all used, and that meat-curing salt is the most common and cheapest. NCRAC also notes salt is a drug of low regulatory priority for the US Food and Drug Administration, with no withdrawal time before fish are sold. An accurate kitchen or postal scale is part of the kit (NCRAC).
What this page doesn't cover yet
- The UF/IFAS salt document (VM-86, 'The Use of Salt in Aquaculture', EDIS VM007) now returns 'gone' on EDIS, so the Purdue/NCRAC fact sheet stands in as the extension source. Search snippets of the UF/IFAS page mentioned species cautions (for example tetras and elephantnose fish should not be kept in salt) and a chloride-to-nitrite ratio of 6 to 1; these were not read in full and are not used.
- Conflict: SRAC 452 (fish-only systems) recommends keeping 0.02 to 0.2 percent salt in recirculating water at all times; SRAC 454 and FAO say salt in an aquaponic system harms plants. The page follows the aquaponics sources.
- No source says whether iodised salt or salt with anti-caking agents is safe; NCRAC lists table salt among the forms used without comment.
- No Florida-specific source on salt use; florida_note left null. FWC or FDACS rules on treating food fish were not checked.
- The NCRAC PDF is a scan; its first author's name extracts as 'L. Swarm' (Illinois-Indiana Sea Grant, Purdue) and may be an OCR error. Check the PDF before printing a byline.