Fish Hatchery Management - fisheries & aquaculture

328 FISH HATCHERY MANAGEMENTFIcune 98. Characteristic signs of whirling disease in older fish that have survivedthe disease are a sunken cranium, misshapen opercles, and scoliosis of thespine due to the destruction of cartilage (arro*). (Courtesy G. L. Hoffman, FishFarming Experimental Station, Stuttgart, Arkansas.)which may not appear for 4 months after infection. In heavy infections,spores readily can be found in wet mounts or histological sections (Figure99). They are ovoidal (front view) or lenticular (in profile), and have twopyriform polar capsules containing filaments at the anterior end.Because of the seriousness of whirling disease, control and treatmentmeasures must be rigorous. Ideally, all earthen rearing units and water suPpliesshould be converted to concrete, followed by complete decontamination offacilities and equipment with high concentrations of such chemicals as sodiumhyprochlorite or calcium oxide. Allow the treated area to stand 4 weeks, cleanthoroughly, and repeat decontamination. New eggs or fry must be obtained from aknown uncontaminated source and raised in spore-free ponds or raceways for thefirst 8 months.PLEISTOPHORASeveral species of Pbistophora infect hatchery fish. As the name of the classMicrosporidea indicates, these are exceedingly small protozoans. Pleistophoraspores are about the size of large bacteria, 3-6 micrometers long andsomewhat bean shaped. Severe infections have been reported in the gills ofrainbow trout and in the ovaries of golden shiners. In golden shiners, theparasites infest up to about half of the ovary and significantly reduce thefecundity of broodstock populations.The only known control for Pbistophora in rainbow trout is prevention.Rainbow trout or their eggs should not be transferred from infected touninfected hatcheries. Broodstocks known to be infected should be phasedout and the rearing facilities decontamination.