FISH HEALTH MANAGEMENT 275 



and Drug Administration) often is used to advantage in treating bacterial 

 infections. 



Chemicals and Their Uses 



SALT BATHS AND DIPS 



Fish infected with bacterial gill disease or external parasites often produce 

 excessive amounts of mucus on their gills and body surface. This is a na- 

 tural response to irritation. The mucus buildup, however, often protects the 

 parasites or bacteria and successful treatment may be difficult. A salt 

 (NaCl) treatment, by one of several means, often is helpful as it stimulates 

 mucus flow, rids the fish of the excess mucus, and helps expose the 

 parasites and bacteria to subsequent chemical treatment. 



Salt baths have some direct effectiveness against a few external proto- 

 zoan parasites, fish lice, and leeches. As a prolonged bath treatment and 

 for use in hauling tanks, salt is used at 1,000-2,000 parts per million 

 (38-76 grams per 10 gallons; 283-566 grams per 10 cubic feet). As a dip 

 treatment for leeches and fish lice, it is used at 30,000 parts per million or 

 3% (2.5 pounds per 10 gallons, 18.7 pounds per 10 cubic feet). Fish are left 

 in the solution for up to 30 minutes or until they show signs of stress. 



FORMALIN 



Formalin (registered by the Food and Drug Administration) is one of the 

 most widely used therapeutic agents in fish culture. It is 37% formaldehyde 

 by weight and should be adjusted to contain 10-15% methanol. Methanol 

 helps to retard formation of paraformaldehyde, which is much more toxic 

 than formalin. Formalin should be stored at temperatures above 40°F be- 

 cause on long standing, and when exposed to temperatures below 40°F, 

 paraformaldehyde is formed. Acceptable formalin is a clear liquid. A white 

 precipitate at the bottom of the container or a cloudy suspension indicates 

 that paraformaldehyde is present and the solution should be discarded. 



Formalin is considered to be 100% active for the purpose of treating fish. 

 It is effective against most ectoparasites, such as species of Trichodina, Cos- 

 tia, and Ichthyophthirius (ich), and monogenetic trematodes. Although it is 

 of little value in treating external fungal or bacterial infections of hatched 

 fish, high concentrations (1,600-2,000 parts per million for 15 minutes) 

 have controlled fungal infections on eggs of trout and catfish. Caution 

 should be used when eggs are treated at these high concentrations. Forma- 

 lin is used widely on fish as a bath treatment at 125-250 parts per million 

 (4.4-8.8 milliliters per 10 gallons; 32.8-65.5 milliliters per 10 cubic feet) for 

 1 hour. However, at these concentrations, water temperature will affect the 



