Fish Hatchery Management - fisheries & aquaculture

FISH HL,ALTH MANAGEMEN'I' 273The method by which the chemical is metered into the inflowing waterwill depend on the equipment available and the type of unit to be treated'Although the constant-flow method is very efficient, it can be expensivebecause of the large volumes of water that must be treated'FEEDING AND INJECTIONTreatment of certain diseases, such as systemic bacterial infections and certaininternal parasite infestations, requires that the drug be introduced intothe fish's body. This usually is accomplished with feeds or injections.In the treatment of some diseases, the drug or medication must be fedor, in some way, introduced into the stomach of the sick fish. This can bedone either by incorporating the medication in the food or by weighing outthe correct amount of drug, putting it in a gelatin capsule, and then insertingit into the fish's stomach with a balling gun. This type of treatment isbased on body weight; standard treatments are given in grams of activedrug per 100 pounds of fish per day' in milligrams of active drug perp";i of body weight, or in milligrams of active drug per kilogram of bodyweight. Medicated food may be purchased commerciallY, o-1 prepared atthe hatchery if only small amounts are needed (Appendix H)' Once feedingofmedicatedfoodisbegun,itshouldbecontinuedfortheprescribedtreatment Period.Large and valuable fish, particularly small numbers of them' sometimescan be treated best with injlctions of medication into the body cavity (intraperitoneal)or into the muscle tissue (intramuscular). Most drugs workmole rapidly when injected intraperitoneally. For both types of injections,but particularly intraperitoneal ones, caution must be exercised to insurethat internal organs are not damaged'The most convenient location for intraperitoneal injections is the base ofone of the pelvic fins. The pelvic fin is partially lifted, and the needleplaced at the fin base and inserted until its tip penetrates the body wall.The needle and syringe should be held on a line parallel to the long axis ofthebodyandatabouta45degreeangledownwardtoavoidinterna]organs (ree Chapter 3, Figure 59). One can tell when the body wall hasbeen pentrated by the sudden decrease of pressure against the needle. As,oon u. the tip of the needle is in the body cavity, the required amount ofmedication should be injected rapidly and the needle withdrawn.intramuscular injections, the best location usually is the area immediatelyahead of the dorsal fin. The syringe and needle should be held on a lineparallelwiththelongaxisofthebodyandatabouta45degreeangledownward. The needle is inserted to a depth of about 1 ,o I inch and themedication slowl\ is injected directly into the muscle tissue of the back'Theinjectionmustbedoneslowly,otherwisebackpressurewillforcethemedicationoutofthemusclethroughthechannelcreatedbytheneedle.For