WILSON ET AL.: EFFECT OF SNAIL ON OYSTERS 



Parasitized 

 4.5 r • 



4.0 



3.5 



B 3.0 



_c 



c 

 o 



CO 



3 



§ 2.0 



CD 

 CO 



^ 1.5 



0) 



1.0 



0.5 



• • • 



100 



-••- 



200 300 



Snail Scale 



400 



500 



Previously Parasitized 



4.5 



4.0 



3.5 



•• 



1.0 



0.5 



• • 



100 200 300 



Snail Scale 



400 



500 



Figure 3.— Left: Intensity oiPerkinsus marinus infection in snail -parasitized oysters as a function of the level of snail parasitism after 

 the 4-wk treatment period. Right: Intensity of P. marinus infection in previously snail-parasitized oysters as a function of the level 

 of snail parasitism after the 4-wk recovery period. 



and previously parasitized oysters. Recovery con- 

 trols had significantly less glycogen in the mantle 

 tissue (Table 7). No biochemical component was 

 significantly correlated with the intensity of snail 

 parasitism (snail scale) in parasitized oysters dur- 

 ing the 4-wk treatment period except taurine in the 

 adductor muscle (Table 9). A similar comparison, 

 using the previously parasitized oysters after the 

 4-wk recovery yielded only two significant correla- 

 tions with snail scale; soluble protein and hypo- 

 taurine content. In addition, lipid phosphate in the 

 mantle tissue and fatty acid content in the adductor 

 muscle were significantly correlated with the inten- 

 sity of Perkinsus marinus infection after the 

 recovery period (all recovery oysters, controls and 

 previously parasitized, were included in the analysis. 

 Table 9). 



DISCUSSION 



Oysters averaged as few as about 3 and as many 

 as 14 snails per day during the 4-wk treatment 

 period; however, only 11% of the oysters had 10 or 

 more snails per day and 76% had fewer than 9 per 

 day. This range of parasitism is typical for many 

 reefs in the experimental area (Copano Bay- Aransas 

 Bay, TX-White et al. 1984; Powell et al. 1987) and 

 corresponds to the lower parasite levels used by 

 White et al. (1988, in press) in laboratory studies 

 on these animals. 



The effects of snail parasitism were minor on a 

 biochemical level, but substantial on an organismal 

 level. Growth, reproductive capacity, and health, as 

 measured by Perkinsus marinus infection, were 

 significantly affected. Other odostomians also re- 



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