Fish Hatchery Management - fisheries & aquaculture

FISH HATCHERY MANAGEMENTthe pectoral fins. The caudal fin may be completely destroyed. A peduncledisease lesion usually starts on the caudal peduncle behind the adipose fin,where it causes inflammation, swelling, and gradual erosion. The diseaseprogresses posteriorly and the caudal fin may be eroded. Coho and chumsalmon are the most susceptible and, in sac fry, the yolk sac may beruptured.Peduncle disease or coldwater disease is caused by a flexibacterium,Cytophaga pslchrophilia. The bacteria are water-borne and can be transmittedfrom carrier fish in the water supply. Crowded conditions stimulate adisease outbreak but are not necessary for the disease to aPPear.The best treatment for peduncle disease is the oral administration ofdrugs with food. Sulfasoxazole (Gantrisin) and sulfamethazine (not registeredby the Food and Drug Administration), at 9 grams per 100 poundsfish per day, or oxytetracycline (Terramycin), at 2'5 grams per 100 poundsof fish per day, should be given for l0-14 days. Chemotherapy combinedwith, or followed by, external disinfection with Roccal will give better andlonger lasting results.F'IN ROl'Advanced cases of fin rot can resemble peduncle disease, but in this diseasebacteria are found in fin lesions only and no specific type of bacterium isrecognized as its cause. Signs may occur incidentally in the course ofanother bacterial disease, such as furunculosis. In typical fin rot, fins firstbecome opaque at the margins and then lesions move Progressively towardthe base. Fins become thickened because of proliferation of tissue and, inadvanced cases, may become so frayed that the rays protrude. The entirecaudal fin may be lost, followed by a gradual erosion of the peduncle.Common water bacteria such as Aeromonas hydrophila and Pseudomlnas sp.often are found in lesions of fin rot. Flexibacteria sometimes are mixedwith other types of bacteria. The disease is associated with poor sanitaryconditions that lead to fin abrasion, secondary bacterial infection, and finallyfin rot.The best results from treatments of fin rot infections are obtained with asoluble form of Terramycin added to water at l0 to 50 Parts per million forI hour. Control also may be achieved with Hyamine or Roccal (not registeredby the Food and Drug Administration) in a concentration of I to 2parts per million for I hour.FURUNCULOSISFish furunculosis, a septicemic disease principally of salmonids, has beenknown since 1894. It was first reported in the United States in 1902 and,since then, virtually all trout and salmon hatcheries have either been