RHIZOCEPHALAN INFECTION IN 



BLUE KING CRABS, PARALITHODES PLATYPUS, FROM 



OLGA BAY, KODIAK ISLAND, ALASKA 



P. T. Johnson, 1 R. A. Macintosh, 2 and D. A. Somerton 3 



ABSTRACT 



An isolated population of blue king crabs, Paralithod.es platypus, in Olga Bay, Kodiak Island, was sampled 

 quarterly during 1980-81. It was found to contain abnormal mature females with degenerate ovaries and/or 

 no sign of having extruded ova following molt. Histological studies of these females and of males and 

 females collected subsequently in April 1982 showed that rhizocephalan internas (roots) were present 

 in up to 50% of the population. Both males and females were infected, but male gonads and secondary 

 sexual characteristics were apparently unaffected. Presence of the rhizocephalan was strongly related 

 to ovarian abnormalities. Evidence suggests that infected females can molt, but do not extrude or retain 

 embryos. The Olga Bay rhizocephalan is not related to Briarosaccus callosus, which parasitizes several 

 species of Alaskan king crabs, including the blue king crab. Externas of the Olga Bay parasite were not 

 found. The possible relationship of this rhizocephalan to the genus Thompsonia, which has minute multi- 

 ple externa that might be missed during gross examination, and the possibility that the blue king crab 

 is an abnormal host that does not allow development of externas are discussed. 



Molting, mating, and extrusion of ova occur annually 

 in red king crabs, Paralithodes camtschatica, and 

 biennially in blue king crabs, P. platypus. Because 

 embryos of both species hatch within about 1 yr, 

 empty embryo cases are carried on blue king crabs 

 in the second year (Powell and Nickerson 1965; Sasa- 

 kawa 1973, 1975; Somerton and Macintosh in press). 

 Somerton and Macintosh (1982) 4 studied an isolated 

 population of blue king crabs in Olga Bay (Kodiak 

 Island, AK) and found abnormal females that were 

 of mature size but lacked external evidence of having 

 extruded eggs or that had apparently degenerate 

 ovaries. This paper reports results of gross and 

 histological examination of blue king crabs from the 

 aberrant Olga Bay population and from three ap- 

 parently normal eastern Bering Sea populations. A 

 rhizocephalan, which was found only in the Olga Bay 

 crabs, appears to be responsible for the abnormal 

 reproductive pattern. 



Northeast Fisheries Center Oxford Laboratory, National Marine 

 Fisheries Service, NOAA, Oxford, MD 21654. 



2 Northwest and Alaska Fisheries Center Kodiak Laboratory, Na- 

 tional Marine Fisheries Service, NOAA, P.O. Box 1638, Kodiak, AK 

 99615. 



3 Northwest and Alaska Fisheries Center, National Marine 

 Fisheries Service, NOAA, 7600 Sand Point Way, N.E., Seattle, WA 

 98115. 



4 Somerton, D. A., and R. A. Macintosh. 1982. Aspects of the 

 life history of the blue king crab (Paralithodes platypus) in Alaska. 

 Document submitted to the annual meeting of the International 

 North Pacific Fisheries Commission, Tokyo, Japan, October 

 1982. 



MATERIALS AND METHODS 



Blue king crabs in Olga Bay were sampled quarter- 

 ly: spring (March-April 1980), summer (June 1980), 

 autumn (October 1980), and winter (January 1981). 

 Seasonal sample sizes ranged from 155 to 229 crabs, 

 and a total of 422 males and 337 females was ex- 

 amined. Both sexes were measured to the nearest 

 millimeter in carapace length (see Wallace et al. 

 1949, for measurement). Carapace lengths ranged 

 from 12 to 162 mm for males and 16 to 143 mm for 

 females. Data were taken on external egg clutches 

 of females by relative volume, color of embryos, and 

 presence or absence of eyespots on embryos. Pres- 

 ence or absence of empty embryo cases on non- 

 ovigerous females was also noted. 



For the purposes of this paper, "oogonia" are stem 

 cells; "oocytes" are developing cells before full 

 maturity; and "ova" are cells that have completed 

 vitellogenesis, have a thick chorion, and are ready 

 for fertilization. "Embryo" refers to an external, fer- 

 tilized, and developing egg or ovum. 



The entire ovary and a pleopod with attached em- 

 bryos or empty embryo cases (if present) were re- 

 moved from each female considered to be mature or 

 in the prepubertal stadium (>68 mm carapace length 

 (CL)). These were preserved in 10% freshwater (river 

 water) Formalin 5 solution buffered with sodium 



5 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Manuscript accepted April 1985. 



FTSHF.RY RTTT.T.KTTN- VOT. 84 NO 1 1986. 



177 



