FISH HEALTH MANAGEMENT 



329 



Because there are no known stocks of golden shiners free of Pleistophora 

 ovariae, proper management is the only answer to this problem. The severi- 

 ty of infections increases with age, so only one-year-old broodstock should 

 be used and all older fish destroyed. 



Trematode Diseases (Monogenetic) 



Monogenetic trematode parasites of fish can complete their life cycles on 

 fish without involving other species of animals. Although the majority are 

 too small to be seen by the naked eye, some species may reach 5 millime- 

 ters in length. The posterior organ of attachment, the "haptor," is used in 

 identification of different genera and species. There often are marginal 

 hooklets around margin of the haptor and either zero, two, or four large 

 anchor hooks. 



Species of the family Gyrodactylidae generally are found on the body 

 and fins of fish, rarely on the gills. These parasites move around freely. 

 The members of this family give birth to live young similar in appearance 

 to the adults. They have no eye spots, 16 marginal hooklets, and two large 

 anchors. 



Species of the family Dactylogyridae are found commonly on the gills of 

 fish. Dactylogyrids lay eggs, and have eye spots, one pair of anchor hooks, 



Figure 99. Stained Myxosoma cerebralis spores in a histological section of 

 cartilage, 875 x magnification. (Courtesy G. L. Hoffman, Fish Farming 

 Experimental Station, Stuttgart, Arkansas.) 



