FISH HEALTH MANAGEMENT 325 



All species of Henneguya are histozoic and localize in specific tissues. In- 

 fections may appear as white cysts within the gills, barbels, adipose fins, 

 skin, gall bladder, connective tissue of the head, subcutaneous tissues, or 

 sclera and muscles of the eye. 



Spores of Henneguya grossly resemble spermatoza; they possess two ante- 

 rior polar capsules and an elongate posterior process (Figure 96) that may 

 or may not separate along the sutural plane. The mode of transmission is 

 believed to be fish-to-fish; no methods of chemical control are known. 



Henneguya salminicola has been found in cysts in the body or musculature 

 of coho, pink, and chinook salmon. Chum salmon also are subject to 

 infection. 



In channel catfish, Henneguya infections are categorized with respect to 

 the tissue parasitized and the site of spore formation. An intralamellar 

 branchial form develops cysts within gill lamellae. A cutaneous form causes 

 large lesions or pustules within the subcutaneous layers and underlying 

 musculature of the skin; a granulomatous form causes large tumor- like le- 

 sions. An integumentary form causes white cysts on the external body sur- 

 face. A gall-bladder form develops within that organ and may obstruct the 

 bile duct. An adipose-fin form localizes solely within the tissue of that fin. 



Spores from catfish infections are similar morphologically and virtually 

 indistinguishable on the basis of shape and dimensions. They closely 

 resemble H. exilis described in channel catfish. 



The intralamellar form is observed commonly among cultured catfish but 

 does not cause deaths. The role of this form as a debilitating agent is 

 suspected but unproven. Spore development occurs within capillaries of gill 

 lamellae or blood vessels of gill filaments. The resultant opaque, spore- 

 filled cysts may be foynd in large numbers and are readily observed in wet 

 mounts. 



The inter lame liar form of Henneguya develops spores within basal cells 

 between gill lamellae (Figure 97). This form, in contrast to the intralamel- 

 lar form, has caused large losses among very young channel catfish. Mor- 

 talities of 95% or more among fingerlings less than 2 weeks old have been 

 reported. Loss of respiratory function accompanies acute infections. Fish 

 exhibit signs of anoxia, swimming at the surface of ponds with flared gill 

 opercula. Infected fish are unable to tolerate handling. Most attempts to 

 treat with parasiticides have resulted in additional losses. 



As with other myxosporidean infections, prevention is the only control 

 measure because no chemical treatment is effective. The disease has been 

 spread from hatchery to hatchery with shipments of infected fingerlings. 

 Confirmation of the interlamellar form in a catfish population may warrant 

 destruction of the infected fish and decontamination of the rearing facilities 

 involved. 



