330 FISH HATCHERY MANAGEMENT 



and 16 marginal booklets. Dactylogyrids are common on warmwater fish 

 while Gyrodactylids are common on both trout and warmwater species. 



GrRODACTTLUS 



Species of Gyrodactylus can be identified by the developing embryo inside 

 the adult as well as by their lack of eye spots. The haptor has two large an- 

 chor hooks and 16 marginal booklets (Figure lOO). These worms are so 

 common on trout that it is unusual to examine fish and not find them. Di- 

 agnosis is made from wet mounts of fin tissue or skin scrapings under a mi- 

 croscope at 35 X or lOOx magnification (Figure 101 ). The parasites may 

 occur in large numbers and cause skin irritation and lesions. Fish with 

 large numbers of Gyrodactylus may appear listless, have frayed fins, and 

 flash frequently. In ponds, they may gather in shallow water in dense 

 schools. On salmonids, these parasites are removed easily by treating the 

 fish with formalin at 167 to 250 parts per million for up to 1 hour, or at 25 

 parts per million in ponds with one or more treatments. Potassium perman- 

 ganate at 2 to 3 parts per million for 1 hour should be tested as an alter- 

 nate treatment for formalin-sensitive trout. 



For warmwater fish, excellent results are obtained with Masoten (re- 

 gistered with the Food and Drug Administration) at 0.25 part per million 

 active ingredient as an indefinite pond treatment. Other good pond treat- 

 ments are copper sulfate at whatever concentration that can be used safely, 

 and formalin at 15-30 parts per million. 



DACTYLOGYRUS 



Dactylogyrus is but one genus of several dactylogyrids found on warmwater 

 fish. These worms are particularly serious parasites of cyprinids. Dactylo- 

 gyrus, a small gill parasite, can be identified by the presence of four eye 

 spots, one pair of anchor hooks, and 16 marginal booklets (Figure lOO). 

 No embryos will be found internally, as these worms lay eggs. These 

 parasites feed on blood and can cause serious damage to the gills of warm- 

 water fish when numerous. Clinical signs easily can be mistaken for those 

 caused by an oxygen deficiency or other gill infections. Dactylogyrids easi- 

 ly are controlled with 0.25 part per million active Masoten, copper sulfate 

 at whatever concentration is safe, or 15-25 parts per million formalin as an 

 indefinite pond treatment. Formalin at 125-250 parts per million for up to 

 1 hour is an effective bath treatment for raceways, tanks, or troughs. 



CLEIDODISCUS 



Cleidodiscus sp. is common on the gills of catfish and a variety of other 

 warmwater fish species. Like Dactylogyrus, it has eye spots, but has four 



