Fish Hatchery Management - fisheries & aquaculture

274 FISH HATcHERY MANAGEMENTGeneralInformationon ChemicalsBecause many drugs and chemicals will be federally registered in the futurefor use at fish hatcheries and historically have successfully controlled fishdiseases, much information is provided in the following section. However,many have not been registered at this time by the United States Food andDrug Administration for use with fishes; reference to unregistered drugsand chemicals in this section and in other chapters of this book should notbe construed as approval or endorsement by the United States Fish andWildlifeService. In all cases where chemicals and drugs are discussed,their registration status is indicated.Chemicals purchased for hatchery use should be of United States Pharmaceutical(USe;ttu6", if possible, and stored in amber containers toprevent deterioration by sunlight. The chemical formula should be on thelabel. Treatment compounds must be stored as directed on the label, andlids or caps always should be tight. If chemicals become abnormal in color,texture, etc., they should be discarded. Poisonous chemicals should be handledonly with proper safety precautions.Antibacterial agents currently used to control bacterial infections in fishinclude sulfonamides, nitrofurans, and antibiotics. The basic principle ofchemotherapy is one of selective toxicity. The drug must destroy or eliminatethe pathogen by either bactericidal or bacteriostatic action withoutside reactions to the host.Treatment of some diseases, such as columnaris, ulcer disease, and furunculosis,requires the feeding of drugs. This is accomplished by mixing thedrug with the fish's food. The amount of drug to be fed is relatively smalland thorough mixing is necessary to insure proper distribution in the feed.Fish should be hungry before medicated feed is administered; therefore, itmay be necessary to eliminate a prior feeding to insure that the treatedfood is taken readily.With the development of dry diets it now is possible to buy medicatedfeed containing the drug of choice. Fish of different sizes require use ofvarying amounts of food and drug, and custom milling may be necessary inorder to deliver the proper dosage.When internal medication is begun, it should be maintained until theprescribed treatment period has been completed. It takes approximately 3days to build up an effective drug level within fish. To maintain the druglevel, the fish should receive only medicated food during the treatmentperiod. Generally, once the medication is started, it is continued for 10-12days or until mortality returns to normal, then extended for at least 3 moredays.Drug combinations sometimes are more efficient than single drugs. Thecombination of sulfamerazine and furazolidone (not registered by the Food