Fish Hatchery Management - fisheries & aquaculture

332 FISH HATCHERY MANAGEMENTFrcuRE 102C leidodiscus sp.large anchor hooks (Figure 102) and lays eggs; unlaid eggs frequently maybe seen within the adult worm. Cleidodiscus is found only on the gillswhere, when numerous, it causes respiratory problems by severely damagingthe tissue. Signs of infection, therefore, are those of gill damage andmay be similar to those seen when oxygen is low.The most effective control is Masoten at 0.25 part per million as a pondtreatment. Other controls include formalin at 15-25 parts per million, 2parts per million potassium permanganate, or copper sulfate at whateverrate can be used safely as an indefinite pond treatment. In raceways, tanks,or troughs, use 125-250 parts per million formalin for up to I 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 majorgroups; (l) those that live in fish as adults, producing eggs that leave thefish to continue the life cycle, and (2) those that penetrate the skin of thefish and live in the fish as larvae, usually encysted in the tissue, until thefish is eaten by the final host.SANGUINICOLABlood flukes(Sanguinicola daaisi) live as adults in arterioles of the gillarches of salmonids and other fish species. These tiny worms lay eggs thatbecome trapped in the capillary beds of the gills and other organs, wherethey develop into miracidia that have a characteristic dark eye spot (Figure103). When fully developed, the ciliated miracidia burst from the gill to beeaten 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 continualtreatment of infected water supplies to kill the cercaria, or eradication of