Fish Hatchery Management - fisheries & aquaculture

FISH HEALTH MANAGEMENT 329Because there are no known stocks of golden shiners free of Pleistophoraouariae, proper management is the only answer to this problem. The severityof infections increases with age, so only one-year-old broodstock shouldbe used and all older fish destroyed.Trematode Diseases (M onogenetic)Monogenetic trematode parasites of fish can complete their life cycles onfish without involving other species of animals. Although the majority aretoo small to be seen by the naked eye, some species may reach 5 millimetersin length. The posterior organ of attachment, the "haptor," is used inidentification of different genera and species. There often are marginalhooklets around margin of the haptor and either zero' two' or four largeanchor hooks.Species of the family Gyrodactylidae generally are found on the bodyand fins of fish, rarely on the gills. These parasites move around freely'The members of this family give birth to live young similar in appearanceto the adults. They have no eye spots, 16 marginal hooklets, and two largeanchors.Species of the family Dactylogyridae are found commonly on the gills offish. Dactylogyrids lay eggs, and have eye sPots' one pair of anchor hooks,ld'.:l..:&".FiEijnr 99. Stained Myxosoma cerebralis spores in a histological section ofcartilage, 875x magnification. (Courtesy G. L. Hoffman, Fish FarmingExperimental Station, Stuttgart, Arkansas.)I