150 



Fishery Bulletin 98(1) 



with the parasite in Tanner crabs and Austrahan 

 sand crabs (Portunus pelagicus) have been partially 

 successful. Parasites from primary cell culture (with 

 sterile hemolymph) were successful in establishing 

 infections in Tanner crabs, but inoculation with vege- 

 tative stages did not produce infections (Meyers et al., 

 1987). Injections of trophonts (vegetative stages) were 

 successful in producing infections in the sand crab, 

 but other stages were not investigated (Hudson and 

 Shields, 1994). Infection experiments with Norway 

 lobster have not been reported. Transmission with 

 cultured dinospores has yet to be achieved (Appleton 

 and Vickerman, 1998). Sporulation is a rapid event 

 with H. perezi, presumably occurring over several 

 hours instead of several days or weeks as reported for 

 Hematodinium sp. from Tanner crabs (Meyers et al., 

 1987, 1990). At lower temperatures and salinities, H. 

 perezi apparently ceases to grow or slows its prolif- 

 eration in naturally infected blue crabs. ^ 



Densities of circulating hemocytes declined rapidly 

 in infected blue crabs. The decline occurred within 

 the first three days and progressed to a 48% decrease 

 in total hemocyte densities within the first week of 

 infection. After three weeks, absolute declines of up to 

 809^ were noted for total hemocyte densities. The loss 

 of cells was evident early in the infection even though 

 the parasites were not detectable in hemolymph. 

 Declines in hemocyte densities have been reported for 

 starved lobsters (33-60% loss) (Stewart et al., 1967), 

 Aeromo/ms-infected lobsters ( 80-84% loss) ( Stewart et 

 al., 1983), Fusarium -miected brown shrimp, Penaeus 

 californiensis (approximately 887c loss) (Hose et al., 



" Messick, G. 1998. Oxford Cooperative Laboratory, 904 S. 

 Morris St., Oxford, MD 21654. Personal, commun. 



1984), and V;'6r/o-infected Cancer irroratus (95% loss) 

 (Newman and Feng, 1982). Reductions in hemocytes 

 were noted for Norway lobster, N. norvegicus, infected 

 with Hematodinium sp. (Field and Appleton, 1995), 

 and for blue crabs, C. sapidus, infected with Par- 

 amoeba perniciosa (Sawyer et al., 1970), but the 

 degree of loss, and differential counts were not quan- 

 tified. Declines in hemocyte counts occur quickly in 

 crayfish, Pacifastacus leniusculus, (10 min) and are 

 associated with loss of resistance to Aphanomyces 

 infections; the declines are dependent upon the stim- 

 uli (yeast vs. zymosan vs. buffers), and are evident 

 over the course of several days (Perrson et al., 1987). 

 Crustacean cell types probably represent matura- 

 tion of a single lineage (e.g. Bodammer, 1978; Bachau, 

 1981; Hose et al., 1990). Hyalinocytes represent 

 younger cells that become semigranulocytes (inter- 

 mediate hemocytes), then granulocytes. Infected 

 crabs exhibited marked shifts in subpopulations of 

 different hemocyte stages (cell types). Because there 

 was an absolute decline in the total number of cir- 

 culating hemocytes and relative declines in hya- 

 linocytes and semigranulocytes, we suggest that 

 cell death and differential sequestration occur in 

 response to the disease. General declines in hemocyte 

 density in A^. norvegicus infected with Hematodin- 

 ium sp. may occur from sequestration, other defense 

 reactions, and hydrostatic effects of heavy infections 

 or clogging of hemal sinuses (Field and Appleton, 

 1995). In our study, the rapid decline in total hemo- 

 cyte density (within three to seven days) argues 

 against hydrostatic effects and clogged sinuses. The 

 shift towards proportionally more granulocytes than 

 hyalinocytes may result from mobilization of tissue- 

 dwelling reserves, differential cell death (Mix and 



