Shields and Squyars: Mortality and hematology of Callinectes sapidus infected with Hematodinium perezi 



151 



Sparks, 1980), changes in mitotic stimuli of hemo- 

 poetic tissue (Hose et al., 1984). or sequestration of 

 specific cell types in defense of the infection (e.g. 

 nodule formation, Johnson, 1976, 1977). Hyalino- 

 cytes and semigranulocytes are the major phagocytic 

 hemocytes in crustaceans (Bachau, 1981; Hose et 

 al., 1990). Such hemocytes form nodules in bacte- 

 rial, amoebic, and Hematodinium infections in blue 

 crabs, Hematodinium infections in A^. norvegicus, 

 and gaffkemia infections in Homarus americanus 

 (Johnson, 1976, 1977; Johnson et al., 1981; Messick, 

 1994; Field and Appleton, 1995) are thus removed 

 from circulation, and may account, in part, for the 

 observed declines. In fungal infections of crayfish, P. 

 leniusculus, hemocytic nodules do not dissociate in 

 the presence of zymosan, a yeast derivative, and may 

 last several days (Perrson et al., 1987). In Aeromo- 

 ?jas-infected lobsters, the hyalinocytes increase in 

 proportion to the other cell types, presumably by 

 increased mitotic activity in hemopoeitic centers, but 

 there is a significant decline in hemocytes after five 

 days of infection (Stewart et al., 1983). 



Lastly, several blue crabs (n =4) successfully fought 

 off the infection. These "immune" crabs exhibited 

 significant sustained levels of granulocytes, did not 

 suffer hemocytopenia, their hemolymph clotted nor- 

 mally, and they did not exhibit gross changes in 

 morbidity. Histological preparations of heart, hepa- 

 topancreas, muscle, and hemopoeitic tissues were 

 negative for latent infections in the "immune" ani- 

 mals. The relative increase in semigranulocytes and 

 sustained densities of hyalinocytes over time (Fig. 5) 

 suggests an increase in mitotic activity in hemopo- 

 etic tissue in response to the infection. This increase 

 may not be sufficient to counter the parasite in sus- 

 ceptible hosts. In A^. norvegicus infected with Hema- 

 todinium sp., the hemopoeitic tissues show marked 

 increases in activity. Although changes in host cell 

 densities were not quantified, apparent stem cells 

 were present in the active nodes (Tables 1 and 2 in 

 Field and Appleton, 1995). The role of the granulo- 

 cytes in the defense against Hematodinium infec- 

 tions and the underlying mechanisms leading to 

 refractory hosts warrant further study. 



Acknowledgments 



We wish to thank Seth Rux and Mike Seebo for their 

 generous help. Seth Rux and members of the VIMS 

 Dredge Surveys ably provided crabs. We thank Mary 

 Anne Vogelbein, Romuald Lipcius, and Morris Rob- 

 erts for technical advice, as well as Mike Newman 

 for assistance with the survival analyses. Gretchen 

 Messick and John Pearce improved the manuscript. 



This work was supported by NOAA, Saltonstall-Ken- 

 nedy Grant NA76FD0148. 



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