'*^- 



«,?■'*> V. 



/•■ 



^r1 



.1 / > \. ' 



r^/ 



■vi: 



v.. 



•■^ 







Figure 5. — Histological sections of oysters: (a) normal, 

 and (b) parasitized by Bucephalus (x 3.5). Note in (b) 

 the almost complete destruction of gonad tissue, which 

 stains darkly in (a). 



Recently, Cheiifj (1965) .md CheiiK and Burton 

 (1965) u.scd histochoniic-al methods to examine 

 the ho.st-para.site relation of the American oy.s- 

 ter and the larval trematode, Bucephalia^ sp. 

 Parasitization cau.sed marked changes in the 

 distribution of fats. 



Larval trematodes of the f.imily Bucephalidae 

 also occur in New Zealand oysters, Ostrca lutarui 

 Hutton. Millar (1963) reported that oy.sters 

 imported from New Zealand and maintained 

 for breeding studies in Scotland were fre- 

 (luently parasitized and that the percentage 

 mortality was much higher among parasitized 

 individuals than among normal ones. We have 

 recently found Pacific oysters from Taiwan to 

 be infected with larval Buicphalus. 



Hyperparasitization of sporocysts of Buceph- 

 alus in American oysters from the Gulf of 

 Mexico was reported by Mackin and Loesch 



(1955). This hyperparasitization produced 

 blackish discoloration of oyster mantle and 

 viscera, and destruction of sporocysts, followed 

 by release of the haplosporidan spores into host 

 oyster tissue. Pronounced cellular reaction was 

 elicited in the localized areas where spores were 

 found in oyster tissue; the authors described 

 some abnormal development of the hyperpara- 

 site in such tissue. The hyperjjarasite was not 

 named, but it was considered on the basis of 

 sjiore morphology to be a haplosporidan dis- 

 tinct from the parasite Vrosporidium pclsoieeri 

 (Caullei\\' and C'haiiellier) found in clams of 

 the genus Douax. 



Sprague (1964) described a microsporidaii 

 hyperparasite, Nosema dollfusi, of Bucephalus 

 and s|)eculated that escape of the jirotozoan 

 into the tissues of the oyster could contribute 

 to the death of the molluscan host. Shuster and 



344 



U.S. FISH AND Wll.nill 1. SLRVICE 



