FISH HEALTH MANAGEMENT 307 



Aeromonas hydrophila. Presently, the Fish Health Section of the American 

 Fisheries Society recommends the name Enteric Redmouth. Enteric red- 

 mouth disease occurs in salmonids throughout Canada and much of the 

 United States. Outbreaks in Pennsylvania trout and in Maine Atlantic sal- 

 mon are among the most recent additions to its geographical range. 



The gram- negative Yersinia ruckeri produce systemic infections that result 

 in nonspecific signs and pathological changes. The diagnosis of infections 

 can be determined only by isolation and identification of the bacterium. 



Enteric redmouth disease is characterized by inflammation and erosion 

 of the jaws and palate of salmonids. Trout with ERM typically become 

 sluggish, dark in color, and show inflammation of the mouth, opercula, 

 isthmus, and base of fins. Reddening occurs in body fat, and in the posteri- 

 or part of the intestine. The stomach may become filled with a colorless 

 watery liquid and the intestine with a yellow fluid (Figure 8l). This disease 

 often produces sustained low-level mortality, but can cause large losses. 

 Large-scale epizootics occur if chronically infected fish are stressed during 

 hauling, or exposed to low dissolved oxygen or other poor environmental 

 conditions. 



The disease has been reported in rainbow trout and steelhead, cutthroat 

 trout, and coho, chinook, and Atlantic salmon. The bacterium was isolated 

 first in 1950, from rainbow trout in the Hagerman Valley, Idaho. Evidence 

 suggests that the spread of the disease is associated with the movement of 

 infected fish to uncontaminated waters. Fish-to-fish contact provides 

 transfer of the bacterium to healthy trout. 



Because spread of the disease can be linked with fish movements, the best 

 control is avoidance of the pathogen. Fish and eggs should be obtained only 

 from sources known to be free of ERM contamination. This can be accom- 

 plished by strict sanitary procedures and avoidance of carrier fish. 



Recent breakthroughs in the possible control of ERM by immunization 

 have provided feasible economic procedures for raising trout in waters con- 

 taining the bacterium. Bacterins on the market can be administered effi- 

 ciently to fry for long-term protection. 



A combination of drugs sometimes is required to check mortality during 

 an outbreak. One such combination is sulfamerazine at 6.6 grams per 100 

 pounds fish plus NF-180 (not registered by the Food and Drug Adminis- 

 tration) at 4.4 grams per 100 pounds fish, fed daily for 5 days. 



MOTILE AEROMONAS SEPTICEMIA (MAS) 



Motile aeromonas septicemia is a ubiquitous disease of many freshwater 

 fish species. It is caused by gram- negative motile bacteria belonging to the 

 genera Aeromonas and Pseudomanas. Two species frequently isolated in out- 

 breaks are A. hydrophila and P. fluorescens. A definitive diagnosis of MAS 



