JOHNSON: MICROSPORIDANS OF AMPELISCA AGASSIZI 



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Figure i.—Ampelisca agassizi: Groups of spores and prespores 

 of the muscle-infecting microsporidan. Bar = 10 fjm. 



sporidan-infected A. agassizi, prevalence was equal 

 to or slightly higher in juveniles than in subadults 

 or ovigerous females. Prevalence was very low in the 

 small sample of adult males, but varied considerably 

 in individual samples of both males and postovi- 

 gerous females (Ikble 3). The three stations with the 

 most consistently numerous populations of A. 

 agassizi also had the highest prevalences of micro- 

 sporidan infection. These were stations 23, 33, and 

 48, with overall prevalences of 30%, 37%, and 22%, 

 respectively. Overall prevalence at other stations 

 ranged from to 14%. 



The majority of infected hosts showed no reaction 

 to the presence of the microsporidans. However, 

 there was occasional melanization in heavily infected 

 muscle, with invasion of hemocytes into the mass of 

 spores, some encapsulation of spores and infected 

 muscle, and lysis of many spores. In these cases, it 

 appeared that the muscle had lost its integrity; that 

 is, the sarcolemma probably was no longer entire 

 Often, other infected muscle near the necrotic mass 

 of spores and muscle showed no evidence of attack 

 by host defense mechanisms. 



The second microsporidan of A. agassizi parasi- 

 tized epithelial cells of the posterior half of the 

 midgut. Juveniles, male and female subadults, and 



ovigerous and postovigerous females were infected. 

 The parasite resembled Nosema, the spores being 

 single and free in the cytoplasm of the host cell (Fig. 

 5). Spores were slightly oval and about 2 ^m in the 

 greater dimension. Infected cells were hypertrophied 

 (Fig. 6). In one heavy infection, many spores were 

 free in the gut and apparently most infected cells 

 had ruptured. There was no host reaction to infec- 

 tion. This parasite occurred twice in individuals with 

 microsporidan infection in abdominal muscle. 

 Based on sectioned material, overall prevalence of 

 the gut microsporidan was < 0.1% (25/2403). 

 Prevalence in samples with one or more infected A. 

 agassizi was 3.7% (25/678), range 1-6%. Amphipods 

 with microsporidans in the gut epithelium were from 

 stations 23, 33, 47, 48, 49, 50, and 51. 



Microsporidans in Species Other Than 

 A. agassizi 



Males and females of Unciola species (probably all 

 U. irrorata Say and U. inermis Shoemaker) were 

 hosts to a microsporidan that infected longitudinal 

 muscles of the pleosoma In three instances, a similar 

 or the same microsporidan was found in a ganglion 

 of the ventral nerve cord, and not in muscla Spores 

 appeared similar to those of the A. agassizi parasite; 

 they measured about 3 x 1.5 ^m; and there were 

 eight or more spores per envelope Unlike the A. 

 agassizi parasite, vegetative stages were often pres- 

 ent along with developed and developing spores. Un- 

 ciola species have an opaque cuticle, and infected 

 muscle cannot be seen grossly. Based on sectioned 



Table 3. — Prevalence of microsporidan infections in Ampelisca 

 agassizi by life-history stages. Stations 47 and 48, cruises E and F. 



Life-history 

 stage 



No. infections/ 

 total collected 

 (% prevalence) 



No. infections/ 

 total collected 

 (% prevalence) 



501 



