FISH HEALTH MANAGEMENT 273 



The method by which the chemical is metered into the inflowing water 

 will depend on the equipment available and the type of unit to be treated. 

 Although the constant- flow method is very efficient, it can be expensive 

 because of the large volumes of water that must be treated. 



FEEDING AND INJECTION 



Treatment of certain diseases, such as systemic bacterial infections and cer- 

 tain internal parasite infestations, requires that the drug be introduced into 

 the fish's body. This usually is accomplished with feeds or injections. 



In the treatment of some diseases, the drug or medication must be fed 

 or, in some way, introduced into the stomach of the sick fish. This can be 

 done either by incorporating the medication in the food or by weighing out 

 the correct amount of drug, putting it in a gelatin capsule, and then insert- 

 ing it into the fish's stomach with a balling gun. This type of treatment is 

 based on body weight; standard treatments are given in grams of active 

 drug per 100 pounds of fish per day, in milligrams of active drug per 

 pound of body weight, or in milligrams of active drug per kilogram of body 

 weight. Medicated food may be purchased commercially, or prepared at 

 the hatchery if only small amounts are needed (Appendix H). Once feed- 

 ing of medicated food is begun, it should be continued for the prescribed 

 treatment period. 



Large and valuable fish, particularly small numbers of them, sometimes 

 can be treated best with injections of medication into the body cavity (in- 

 traperitoneal) or into the muscle tissue (intramuscular). Most drugs work 

 more rapidly when injected intraperitoneally. For both types of injections, 

 but particularly intraperitoneal ones, caution must be exercised to insure 

 that internal organs are not damaged. 



The most convenient location for intraperitoneal injections is the base of 

 one of the pelvic fins. The pelvic fin is partially lifted, and the needle 

 placed 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 of 

 the body and at about a 45 degree angle downward to avoid internal 

 organs (see Chapter 3, Figure 59). One can tell when the body wall has 

 been pentrated by the sudden decrease of pressure against the needle. As 

 soon as the tip of the needle is in the body cavity, the required amount of 

 medication should be injected rapidly and the needle withdrawn. For 

 intramuscular injections, the best location usually is the area immediately 

 ahead of the dorsal fin. The syringe and needle should be held on a line 

 parallel with the long axis of the body and at about a 45 degree angle 

 downward. The needle is inserted to a depth of about 7 to ^ inch and the 

 medication slowly is injected directly into the muscle tissue of the back. 

 The injection must be done slowly, otherwise back pressure will force the 

 medication out of the muscle through the channel created by the needle. 



