JOHNSON ET AL.: RHIZOCEPHALAN INFECTION IN BLUE KING CRABS 



crab females taken from Olga Bay in January 1981. 

 Rhizocephalan externas were never detected. Rhizo- 

 cephalan tissue was not found in any of the 76 blue 

 king crabs collected from the Bering Sea and ex- 

 amined by us. 



Data on females collected from Olga Bay in 

 January 1981 and April 1982 were combined and 

 then separated into various categories of reproduc- 

 tive condition, based on both histological condition 

 and reproductive features of the ovary and on ex- 

 ternal reproductive features. Females in all cate- 

 gories were further classified by the presence or 

 absence of rhizocephalan infection, as determined 

 histologically (Table 3). 



The effect of the rhizocephalan on female repro- 

 duction was examined by testing the independence 

 of probable future reproductive success and rhizo- 

 cephalan presence Based on ovarian categories 

 (Table 3), probable future reproductive success was 

 judged as either successful (no degenerating gonadal 

 cells) or unsuccessful (ovary empty or ovary with 

 degenerate gonadal cells). Independence of probable 

 future success and rhizocephalan presence was re- 

 jected for both measures, implying that rhizo- 

 cephalan infestation significantly reduces the prob- 

 ability of future reproductive success (x 2 = 16.81, 

 df = 1, P < 0.001 for empty ovary; x 2 = 20.41, df 

 = 1, P < 0.001 for ovary with degenerate gonadal 

 cells). 



Three of the external categories of females (Table 

 3) represent crabs at different times after extrusion 

 of ova. Embryos begin to develop eyes about 4 mo 

 after extrusion. Hatching occurs slightly more than 

 12 mo after extrusion. Following hatching, empty 

 embryo cases persist on the pleopod setae until the 

 crab molts again, usually slightly <12 mo later 

 (Somerton and Macintosh in press). Therefore, the 



Table 3.— Prevalence of rhizocephalan infection in female blue 

 king crabs (>68 mm CL) collected in Olga Bay, Kodiak Island, 

 AK, January 1981 and April 1982. 



'Oocytes and/or ova. 



generalized time since extrusion for the uneyed, 

 eyed, and empty-embryo-case categories is 0-4 mo, 

 4-14 mo, and 14-24 mo, respectively. If parasitic at- 

 tacks are random and prevent successful extrusion 

 and embryo attachment, then prevalence of the 

 parasite should be low for females with uneyed em- 

 bryos and should increase with time Independence 

 between prevalence and time since extrusion (using 

 uneyed and empty-embryo-case categories) was re- 

 jected (x 2 = 7.79, df = 1, P < 0.01). 



Females are grasped by males and held in a "pre- 

 copulatory embrace" before molting and mating. Of 

 the 10 grasped females collected January 1981, 5 

 showed no evidence of previous reproductive activity, 

 and 5 had empty embryo cases. None were infected 

 with the rhizocephalan, although three of the 

 females with empty embryo cases had some degen- 

 erate gonadal cells. 



Based on the April 1982 sample, which includes 

 males, independence between sex and rhizocephalan 

 presence was not rejected (x 2 = 0.14, df = 1, P = 

 0.75). The rhizocephalan, therefore, does not appear 

 to discriminate by host sex. 



Presence of the rhizocephalan apparently did not 

 affect the gonads of males. Both infected and non- 

 infected males had numerous spermatophores in the 

 anterior vas deferens. Spermatocytes, some of them 

 dividing, and developing and mature sperm were 

 present in the four crabs whose testes were sampled 

 (one parasitized and three nonparasitized). In the 

 field, we saw no males exhibiting female secondary 

 sexual characteristics. 



Histological Observations 



Rhizocephalan roots occupied the hemal spaces of 

 the pleopods, were associated with the exterior of 

 the ovary, and occasionally lay within internal hemal 

 spaces of the ovary of infected females collected in 

 January 1981. Roots were associated with various 

 tissues of males and females collected from Olga Bay 

 in April 1982 (Table 2). Hemal sinuses of the ovary 

 and those abutting the gut, the bladder, and the 

 thoracic ganglia were the most frequently invaded 

 sites. Roots lay within the glia of the thoracic ganglia 

 of one crab, but otherwise were confined to hemal 

 spaces and did not invade tissues. 



Roots were cylindrical and surrounded by a PAS- 

 positive cuticle of variable thickness (Figs. 1, 3). Cells 

 within the roots usually had large vesicular nuclei, 

 and refractile spherules were sometimes present in 

 the cytoplasm. Usually the roots were tubular, with 

 a defined lumen, and those with large, empty lumens 

 often had a flattened epithelium. Loosely anasto- 



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