Somerton and Donaldson: Parasitism of Lithodes aequispinus by two species of Careproctus 
883 
snailfish live in deeper waters and must migrate into 
shallower water to find suitable hosts. For red 
snailfish, a spawning migration is apparent by the 
shallower peak in the depth distribution of its egg 
masses (350 m; Fig. 8) compared with the depth dis- 
tribution of the fish themselves (650 m; Fig. 5). For 
pink snailfish, by comparison, the depth distributions 
of the egg masses and fish nearly coincide. If the 
spawning migration is undertaken only by ripe fish, 
then a difference in depth distribution between ripe 
and unripe fish would be expected for red snailfish 
but not for pink snailfish. We are unable to account 
for our observation that the expected shift in depth 
distribution was found for pink snailfish but not red 
snailfish. 
One shortcoming of the 1982 sampling of snailfish 
eggs and larvae is that the species identification was 
based on an apparent species difference in egg and 
larvae size. Although larvae were collected in an at- 
tempt to establish identification by linking larval 
characteristics to adult fish, the larvae were poorly 
ossified and their identities could not be determined. 1 
In a second attempt at species identification, we sub- 
jected the eggs and larvae collected in the 1996 sam- 
pling to RFLP analysis. On this basis, it was pos- 
sible to establish that pink snailfish do deposit eggs 
in golden king crab. Unfortunately, we had no red 
snailfish tissue available to establish an identifica- 
tion pattern for the RFLP analysis because red 
snailfish were not captured during the 1996 sam- 
pling (the commercial crab fishery does not extend 
into sufficiently deep water). Therefore, it was not 
possible to determine if the 8 of 10 specimens not 
matching any of the three sampled Careproctus spe- 
cies were, as we suspect, red snailfish. 
Damage to the gills from the presence of egg 
masses may result from two causes. First, gill com- 
pression could be strong enough to restrict blood flow, 
resulting in localized necrosis. Second, egg masses 
could interfere with the functioning of the fifth pereio- 
pod (Fig. 10), which is covered with setae and func- 
tions as a gill-cleaning appendage (Pohle, 1989). 
Experiments with other lithodid crabs have demon- 
strated that gill fouling similar to the discoloration 
observed in golden king crab could be experimentally 
produced either by restricting the movement of the 
fifth pereiopod or removing the setae from this ap- 
pendage. The fouling is due not only to the accumu- 
lation of detritus on the gill surface, but also the ac- 
cumulation of a host of organisms that feed on the 
detritus or directly on the gill tissue itself (Pohle, 
1989). In golden king crabs, the degeneration of the 
gill tissue can proceed to the point that all of the gill 
tissue on the infested side is missing (Fig 10). In cases 
of small to medium lesions, it was clear from histo- 
logical examinations that gill regeneration would 
occur at the next molt, but crabs with extreme cases 
of gill degeneration were not examined histologically 
and it is not known whether gill regeneration would 
occur. However, in at least one case, a newly molted 
golden king crab was encountered with no gills on 
one side of the body. Perhaps, this crab was an ex- 
treme case of gill damage which did not regenerate. 
Gill damage not only influences a crab’s respiration 
but also its capability for ion exchange. Lithodid crabs 
that died as the result of the restriction of their clean- 
ing appendages displayed considerable abdominal 
swelling which is indicative of ion imbalance ( Pohle, 
1989). 
The 35% higher mortality of infested male crabs, 
compared with uninfested crabs, within the live tanks 
of commercial vessels (Table 4) indicates that the 
presence of egg masses hinders the ability of crabs 
to withstand the stress of capture and confinement. 
The impact on the fishery, however, depends on the 
incidence of snailfish eggs and larvae as well as the 
additional mortality they induce. In the case of the 
1996 incidence in the Bering Sea (8.5%, Table 3, cor- 
rected for deadloss), for example, live-tank mortal- 
ity increased by only 0.08%. Even at the higher inci- 
dence found in 1982 (44%), additional live-tank mor- 
tality would have been only 0.40%. Although the 
mortality that is induced on wild crabs is unknown, 
it appears that the impact of snailfish parasitism on 
the golden king crab fishery is small. 
Acknowledgments 
We thank Brad Stevens, Jay Orr, Morgan Busby, and 
Doug Pengilly for reviewing the manuscript; Susie 
Byersdorfer for laboratory analysis; and A1 Shimada 
for helping the senior author with the 1981 collec- 
tion of crab and snailfish samples and for providing 
the photograph of the red snailfish. 
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