DISEASE CONTROL 



red with some small hemorrhages. 

 The intestine also may show con- 

 gestion. Scales may stand out on 

 the swollen fishes. Ps. hydrophila 

 can be isolated from the abdominal 

 fluid, blood, and lesions, and iden- 

 tified by a bacteriologist. Frogs 

 also sometimes become infected 

 with this bacterium, and the result- 

 ing disease is called "red leg," 

 stressing the most characteristic 

 symptom of this disease in frogs. 



There is no known treatment for 

 this disease. If fish are in an 

 aquarium or a tank, addition of 

 chloramphenicol may be used. 

 Also feeding food that contains 

 chloramphenicol or terramycin 

 may be effective (see Prolonged 

 and Internal Treatments, pp. 54 

 and 56). 



Fmmnculosis. — Produced in fish 

 by Bactermm. salmonicida^ this is 

 a disease of salmonid fishes (sal- 

 mon and trout), but whenever min- 

 nows or other warm-water fishes 

 are kept in water which flows from 

 tanks or ponds holding infected 

 trout, it may cause severe mortality 

 among them. Furunculosis has 

 variable symptoms. In minnows, 

 the most typical signs are boils or 

 bloodshot fins. Diagnosis can only 

 be made with certainty by bacterio- 

 logical examination of the diseased 

 fishes. Furunculosis, if correctly 

 diagnosed, can be effectively treated 

 by feeding the infected fish with 

 food containing sulfamerazine, or 

 sulfamethazine. Some authors 

 recommend replacement of one- 

 third of either of these two sul- 

 fonamides with sulfaguanidine. 



which belongs to the same group 

 of drugs. Recommended dosage is 

 8 to 10 grams of sulfonamides daily 

 per 100 pounds of fish (see In- 

 ternal Treatment, p. 56). 



Parasitic worms 



Black grub. — Black grub, or 

 black spot, is caused by the larval 

 form of the flatworm, Neascus sp. 

 The jiarasite occurs on fishes as a 

 small black spot about 1^5 of an 

 inch in diameter. This black cyst 

 encloses a small worm which is usu- 

 ally limited to the scales and in- 

 tegument, but wdiich may occasion- 

 ally be found in the flesh just below 

 the skin. The life history of the 

 black grub is complicated, but is 

 typical of many of the parasitic 

 flatworms. The adult worm oc- 

 curs in the kingfisher. Eggs of the 

 Vvorm are discharged into the water, 

 where they hatch into small, free- 

 swimming organisms. These lar- 

 val forms swim about until they 

 come in contact W'ith a particular 

 species of snail. Then they bore 

 into the snail and reproduce them- 

 selves many times. Finally, num- 

 bers of free-swimming forms break 

 out in the water and move about 

 until contact with a fish is made. 

 They then bui-row in and encyst in 

 the scales or in the flesh. When 

 the fish is eaten by a kingfisher, the 

 encysted worm develops into an 

 adult and the life cycle is com- 

 pleted. It usually causes little dam- 

 age to the fish, but may, at times, 

 be jn*esent in numbers large enough 

 to cause death. 



Klak (1940) reports a heavy 



59 



