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		The Use of Salt in Aquaculture
		Page 2 of 5	Pages: 1 . 2 . 3 . 4 . 5
		THE USE OF SALT AS A PARASITICIDE Used in proper amounts, salt effectively controls protozoans on the gills and skin of fish. In many instances, however, too little salt is used, rendering the treatment ineffective. The duration of treatment is used to determine the appropriate salt concentration. A 3 percent salt dip effectively removes protozoa from the skin, gills, and fins of freshwater fish; it also enhances mucus production. Depending on the species, fish can remain in a 3 percent salt solution from 30 seconds to 10 minutes. In general, fish should be left in the salt solution until they lose equilibrium and roll over. When this happens, the fish should be quickly removed from the salt solution and placed in clean, untreated water. Because some species (notably, some tetras) do not tolerate salt well, a bioassay (a test to determine safe concentration) should be conducted before large numbers of these fish are treated. A similar benefit may be obtained by dipping marine fish in fresh water. Marine protozoa burst when placed in fresh water, effectively removing them from the external surfaces of fish. Marine fish should be left in fresh water for no more than 10 minutes, then returned to a clean seawater environment. If dipping is not feasible, freshwater fish may be placed in a brackish water (i.e., 1 percent salt) solution for 30 minutes up to several hours. This procedure produces the same effects as a saltwater dip; that is, it removes external parasites (protozoa) and enhances mucus production. It also benefits fish recovering from skin wounds. Finally, a light solution of 0.01 to 0.2 percent salt may be used as a permanent treatment in recirculating systems. Such levels are quite effective in eliminating single-cell protozoans. Most fish can tolerate prolonged exposure to salt at these concentrations; however, tetras and fish that navigate by electrical field (e.g., elephant nose) should not be maintained in salt. THE USE OF SALT TO TRANSPORT OR HANDLE FISH When freshwater fish are transported and handled, they are forced to expend extra energy for osmoregulation (water balance) unless salt is added to the transport water. Freshwater fish tend to overhydrate when held in fresh water during shipping, due to the influx of water across the gills and into the bloodstream. To compensate for this water imbalance, fish pump excess water back across their gills. Increasing the salt concentration of the transport water inhibits this process, making depletion of energy reserves less likely. Salt may be added to the transport water to increase salinity from 0.1 to 0.3 percent (1,000 to 3,000 ppm, or 3.8 to 11.4 g/gal), minimizing the osmoregulatory stress on fish during shipment. If fish are being transported from one site to another -- for example, from a pond to smaller tanks or vats within a building -- salt may be added to the receiving water. An easy way to accomplish this is to add a small amount of water to the receiving tank, then add salt to create a 3 percent solution (30 ppt or 30,000 ppm); when fish are added to the tank, it should be filled with water. Short-term exposure to a high concentration of salt produces an anti-parasitic effect; longer exposure to a lower concentration of salt helps to stabilize osmoregulation and increase production of the mucus covering the skin, which may have become damaged during handling. more ...

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