NOTE Moles et a L Metazoan parasites as markers for Sebastes 
915 
Table 2 
Comparison of mean parasite intensity by area for shortraker and rougheye rockfishes in the Gulf of Alaska, 1990. Range of 
intensity is in parentheses. Significance probability for differences in intensity and for intensity per cm fish length between areas 
is also given (Mann-Whitney U test). Asterisks indicate P < 0.10. Dash means insufficient number of infected fish to perform 
statistical tests. Int = intensity. 
Significance 
Mean parasite intensity (no. of parasites per infected fish) probability 
Shumagin 
Chirikof 
Kodiak 
Yakutat 
Southeast 
Intensity 
Int/cm 
Shortraker rockfish 
Neobrachiella robusta 
2.4 (1-9) 
7.6 (1-18) 
4.9 (1-12) 
4.4 (1-17) 
3.8 (1-8) 
0.029* 
0.016* 
Naobranchia occidentalis 
0 
1 (1) 
1 (1) 
4.5 (4-5) 
0 
0.333 
0.156 
Chondracanthus pinguis 
1 (1) 
3 (3) 
3.5 (3-4) 
1 (1) 
1.5 (1-2) 
0.131 
0.189 
Colobomatus kyphosus 
0 
0 
0 
1 (1) 
0 
— 
— 
Trochopus trituba 
3.8 (1-9) 
4.8 (1-9) 
16 (1-106) 
17 (2-89) 
8.3 (1-15) 
0.001* 
0.002* 
Microcotyle sebastis 
1.3 (1-2) 
2.5 (2-3) 
0 
0 
0 
0.133 
0.083* 
Corynosoma sp. 
3.3 (1-6) 
2.3 (1-12) 
2.7 (1-7) 
5.6 (1-26) 
3.7 (1-7) 
0.024* 
0.019* 
Echinorhynchus gadi 
1 (1) 
0 
0 
3 (3) 
0 
— 
0.221 
Clavella parva 
1.2 (1-2) 
1.5 (1-5) 
1.5 (1-3) 
1.5 (1-2 
1.3 (1-2) 
0.259 
0.357 
Rougheye rockfish 
Neobrachiella robusta 
2.6 (1-4) 
2.7 (1-7) 
1.8 (1-4) 
5.2 (1-32) 
1 (1) 
0.667 
0.478 
Naobranchia occidentalis 
0 
0 
0 
1 (1) 
0 
— 
— 
Chondracanthus pinguis 
1 (1) 
0 
0 
9.6 (1-61) 
2.7 (1-5) 
0.235 
0.211 
Colobomatus kyphosus 
0 
0 
0 
3 (2-4) 
1.5 (1-2) 
0.333 
0.121 
Trochopus trituba 
4.6 (1-19) 
1.7 (1-3) 
2.1 (1-8) 
9.1 (1-50) 
1.8 (1-3) 
0.023* 
0.069* 
Microcotyle sebastis 
1(1) 
0 
0 
1 (1) 
0 
— 
— 
Corynosoma sp. 
6 (1-17) 
5.1 (1-15) 
4.6 (1-8) 
5 (1-17) 
3.8 (1-7) 
0.973 
0.916 
Echinorhynchus gadi 
0 
0 
1 (1) 
0 
1(1) 
1.000 
0.180 
Clavella parva 
1.4 (1-3) 
1 (1) 
1 (1) 
1.8 (1-3) 
2.2 (1-5) 
0.427 
0.443 
on the host, have a long life span, and be present in 
only one part of the host. Based on coincident 
samples, it is clear that the monogenetic trematodes 
and copepods on the gills of the rockfishes in our 
study meet all these criteria, as do the visceral acan- 
thocephalans. Gill parasites are protected by the 
operculum during capture, are sampled easily, and 
can be identified aboard ship. Notably, Leaman and 
Kabata ( 1987) previously proposed using N. robusta 
as a marker for separating stocks of S. alutus in Brit- 
ish Columbia. Acanthocephalans, such as Coryno- 
soma sp., also serve as excellent markers because 
they can be easily enumerated with a pepsin enzyme. 
In contrast, the lack of digenes and cestodes in the 
preliminary survey (probably due to regurgitation 
through barotrauma) makes these parasites poor 
candidates as tags for deepwater rockfishes. The 
nematodes are difficult to identify and their 
prevalences were similar throughout the Gulf of 
Alaska. 
In addition to their potential use in determining 
stock structure, differences in prevalence between 
areas among the parasites in this study also give 
insight on differences in diet and parasite distribu- 
tions. Corynosoma sp. is widely distributed in the 
northeastern Pacific Ocean as a parasite of marine 
mammals, birds, and fishes (Margolis, 1958); thus 
the different prevalences of Corynosoma sp. in our 
study were likely due to differences in diet rather 
than to parasite distribution. The intermediate hosts 
for Corynosoma sp. are amphipods; hence, the per- 
centage of amphipods in the diet may be higher in 
the western part of the GOA than in the eastern part. 
Alternatively, rougheye and shortraker rockfishes 
may be more likely to consume infected amphipods 
than other prey items. In contrast, both copepods and 
monogenes have no intermediate host stage, and dif- 
ferences in parasitism between management areas 
probably reflect differences in parasite distribution 
or host habitat, rather than differences in diet. 
Some of the parasite species reported in this study 
had very different prevalences than those reported 
for other species or locations of rockfishes. For ex- 
ample, Corynosoma sp. was less prevalent (<10%) in 
most species of British Columbia rockfishes (Sekerak, 
1975; Stanley et al., 1992) than in our study. 
Corynosoma sp. may be more common in the GOA 
than in Canada or simply more prevalent in short- 
raker and rougheye rockfishes than in some other 
species. Sekerak (1975) examined 536 rockfishes of 
