Fish Hatchery Management - fisheries & aquaculture

FISH HEALTH MANAGEMENT 307Aeromonas hldrophila. Presently, the Fish Health Section of the AmericanFisheries Society recommends the name Enteric Redmouth. Enteric redmouthdisease occurs in salmonids throughout Canada and much of theUnited States. Outbreaks in Pennsylvania trout and in Maine Atlantic salmonare among the most recent additions to its geographical range.The gram-negative Tersinia ruckeri produce systemic infections that resultin nonspecific signs and pathological changes. The diagnosis of infectionscan be determined only by isolation and identification of the bacterium.Enteric redmouth disease is characterized, by inflammation and erosionof the jaws and palate of salmonids. Trout with ERMtypically becomesluggish, dark in color, and show inflammation of the mouth, opercula,isthmus, and base of fins. Reddening occurs in body fat, and in the posteriorpart of the intestine. The stomach may become filled with a colorlesswatery liquid and the intestine with a yellow fluid (Figure 81). This diseaseoften produces sustained low-level mortality, but can cause large losses.Large-scale epizootics occur if chronically infected fish are stressed duringhauling, or exposed to low dissolved oxygen or other poor environmentalconditions.The disease has been reported in rainbow trout and steelhead, cutthroattrout, and coho, chinook, and Atlantic salmon. The bacterium was isolatedfirst in 1950, from rainbow trout in the Hagerman Valley, Idaho. Evidencesuggests that the spread of the disease is associated with the movement ofinfected fish to uncontaminated waters. Fish-to-fish contact providestransfer of the bacterium to healthy trout.Because spread of the disease can be linked with fish movements, the bestcontrol is avoidance of the pathogen. Fish and eggs should be obtained onlyfrom sources known to be free of ERM contamination. This can be accomplishedby strict sanitary procedures and avoidance of carrier fish.Recent breakthroughs in the possible control of ERM by immunizationhave provided feasible economic procedures for raising trout in waters containingthe bacterium. Bacterins on the market can be administered efficientlyto fry for long-term protection.A combination of drugs sometimes is required to check mortality duringan outbreak. One such combination is sulfamerazine at 6.6 grams per 100pounds fish plus NF-I80 (not registered by the Food and Drug Administration)at 4.4 grams per 100 pounds fish, fed daily for 5 days.MOTILE AEROMONASEPTICEMIA (MAS)Motile aeromonas septicemia is a ubiquitous disease of many freshwaterfish species. It is caused by gram-negative motile bacteria belonging to thegenera Aeromonas and Pseudomanas. Two species frequently isolated in outbreaksare A. hydrobhila and P. fluorescens. A definitive diasnosis of MAS