OPERATING THE HATCHERY 



15,000 solution (Vs ounce in 15 gal- 

 lons of water) is very effective (see 

 also Flushing, p. 52). 



Bacterial diseases 



Fin rot. — This disease may be 

 caused by several different bacteria. 

 The disease is cliaracterized by a 

 progressive degeneration of a fin or 

 the tail of a fish until the entire 

 appendage is destroyed. The infec- 

 tion starts at the free end of the fin. 

 The diseased tissue is separated 

 from the uninvaded tissue by a 

 white line. Control of this disease 

 is accomplished by dipping in a 

 1 : 2,000 solution of copper sulfate 

 for 1 or 2 minutes. If the water is 

 hard, 10 milliliters of glacial acetic 

 acid should be added to 10 gallons 

 of water (1 fluid ounce to 30 gal- 

 lons) . Fish on which the disease has 

 progressed to a marked degree 

 should be destroyed, as the dip can 

 do little for them. Bacterial fin rot 

 has also been controlled with a 

 1 : 4,000 (8 ounces to 100 gallons of 

 water) solution of formalin (see 

 Prolonged Treatment, p. 54). 



Cohmmaris. — During recent 

 years, many outbreaks of infections 

 of warm-Avater pond fishes with a 

 bacterium called Chondrococcus 

 {C'ytophaga) columnarlH have been 

 reported. This bacterium attacks 

 fish mostly at higher water tem- 

 peratures, like 25° to 30° C. (77° 

 to 88° F.). The infection is 

 chai-acterized by the appearance of 

 grayish-white spots on the head, 

 gills, fins, or some part of the body, 

 wliicli is usually surrounded by a 

 zoiH' with a distinct reddish tinge. 



Superficially, the spots resemble 

 lesions produced by Saprolegnia., 

 but a close inspection shows that 

 they lack the fuzzy appearance so 

 characteristic of a fungus infection. 

 C. columnaris can easily be identi- 

 fied under the microscope by an ex- 

 perienced person. Disease breaks 

 out most frequently as a result of 

 handling, and this can be prevented 

 by dipping the fish right after han- 

 dling for 1 minute in a solution of 

 copper sulfate. This chemical add- 

 ed to pond water at a rate of 1 

 p. p. m. may arrest the progress of 

 the disease. 



Infections dropsy. — Pseudomonas 

 {Aeromonas) hydrophila.^ a bac- 

 terium commonly present in water, 

 causes this disease. Occasionally 

 more infective races (mutants) of 

 this bacterium appear, which are 

 more destructive to fishes. The re- 

 sistance of fishes is lessened by han- 

 dling, crowding, or other unfavor- 

 able conditions. Outbreaks of in- 

 fectious dropsy occur most fre- 

 quently in spring when the tem- 

 perature of water rapidly increases 

 and fish are still weakened by win- 

 ter. Sometimes up to 80 percent 

 of the fish may die within several 

 days. It is one of ihe most de- 

 structive bacterial diseases of warm- 

 water fishes. 



The symptoms of this disease are 

 variable. Sometimes the diseased 

 fish may have deep boils or shallow 

 ulcers on their bodies. Frequently 

 the body is swollen and the abdo- 

 men filled with a watery fluid 

 (dropsy). Occasionally the skin 

 on the abdomen may become pink or 



58 



