332 



FISH HATCHERY MANAGEMENT 



Figure 102. Cleidodiscus sp. 



large anchor hooks (Figure 102) and lays eggs; unlaid eggs frequently may 

 be seen within the adult worm. Cleidodiscus is found only on the gills 

 where, when numerous, it causes respiratory problems by severely damag- 

 ing the tissue. Signs of infection, therefore, are those of gill damage and 

 may be similar to those seen when oxygen is low. 



The most effective control is Masoten at 0.25 part per million as a pond 

 treatment. Other controls include formalin at 15-25 parts per million, 2 

 parts per million potassium permanganate, or copper sulfate at whatever 

 rate can be used safely as an indefinite pond treatment. In raceways, tanks, 

 or troughs, use 125-250 parts per million formalin for up to 1 hour. 



Trematode Diseases (Digenetic) 



Digenetic trematodes require one or more animal hosts, in addition to fish, 

 to complete their life cycles. These parasites can be divided into two major 

 groups; (l) those that live in fish as adults, producing eggs that leave the 

 fish to continue the life cycle, and (2) those that penetrate the skin of the 

 fish and live in the fish as larvae, usually encysted in the tissue, until the 

 fish is eaten by the final host. 



SANGUINICOLA 



Blood flukes (Sanguinicola davisi) live as adults in arterioles of the gill 

 arches of salmonids and other fish species. These tiny worms lay eggs that 

 become trapped in the capillary beds of the gills and other organs, where 

 they develop into miracidia that have a characteristic dark eye spot (Figure 

 103). When fully developed, the ciliated miracidia burst from the gill to be 

 eaten by an operculate snail, the only intermediate host in the life cycle. 

 Cercaria emerge from the snail and penetrate fish to complete the cycle. 



The control of blood flukes is difficult. It depends upon either continual 

 treatment of infected water supplies to kill the cercaria, or eradication of 



