NOTE Moles et a I.: Metazoan parasites as markers for Sebastes 
913 
Northeastern Pacific Ocean, showing management areas of the Gulf of Alaska. 
Asterisks show sampling stations along the continental slope. 
ing for dependence of parasite prevalence 
and intensity by area. Fish size was cho- 
sen as a variable because the size of fish 
sampled in some areas differed, and fish 
size may influence parasite prevalence 
and intensity (Sekerak, 1975). A probabil- 
ity of 0. 10 or less was judged to be statis- 
tically significant. 
Results 
Seventeen species of parasites were 
found in our preliminary examinations: 
six species of copepod on the gills and fins 
and in the cephalic canal and nasal cavi- 
ties; two species of monogenetic trema- 
todes on the gills; three species of dige- 
netic trematodes, two species of acantho- 
cephalans, one species of cestode, and 
three species of nematodes in the viscera 
and mesenteries. All these species had 
been described previously from north- 
eastern Pacific rockfishes, although para- 
sites of shortraker and rougheye rockfishes in the 
western GOA had not been described previously. 
Many of the fish contained both larval nematodes 
Contracaecum spp. and Hysterothylacium spp. Be- 
cause it is time consuming to separate these two gen- 
era, they were lumped together as a single species 
as Contracaecum- type spp. On the basis of these pre- 
liminary results, nematodes, digenes, and cestodes 
were eliminated from further examination. These 
helminths were infrequent in the samples or showed 
no difference between management areas. Further 
examinations focused on enumeration of copepods, 
acanthocephalans, and monogenes. 
Prevalence (Table 1) and intensity (Table 2) of sev- 
eral parasite species differed distinctly among 
shortraker and rougheye rockfish populations in the 
GOA; they varied between areas, rather than being 
present in one area and absent in another. Three of 
these — Neobrachiella robusta (copepod), Trochopus 
trituba (monogenetic trematode), and Corynosoma 
sp. (acanthocephalan) — had the most distinctive 
changes in prevalence between areas. For shortraker 
rockfish, the highest prevalence of N. robusta and T. 
trituba parasites was in Kodiak samples. In rougheye 
rockfish, prevalence of all three parasites was sig- 
nificantly reduced in the Southeast. Several species 
of parasites were scarce in some areas and absent in 
others. 
Of the six species of copepods in our survey, the 
gill copepod N. robusta was sufficiently prevalent to 
be potentially useful in stock discrimination stud- 
ies. Prevalence of N. robusta differed significantly 
between areas for both shortraker (P=0.076) and 
rougheye (P=0.087) rockfish. Neobrachiella robusta 
was present in 80% of the Kodiak shortraker rock- 
fish sampled as opposed to 35-55% of those sampled 
in the other four areas. Larger rougheye rockfish also 
had a significantly (P=0.028) greater prevalence of N. 
robusta than smaller specimens. Among shortraker 
rockfish, intensities ranged from a mean of 2.4 in 
Shumagin to 7.6 in Chirikof; the differences were also 
significant between areas (P=0.029), especially when 
corrected for the size of the fish (P=0.016). Among 
rougheye rockfish, however, intensity of N. robusta 
infection did not differ between areas (P= 0.667). 
Mean infection levels were lower among rougheye 
rockfish than among shortraker rockfish for N. ro- 
busta but still averaged 1-5 parasites per fish. 
Other copepods were prevalent in the GOA 
samples. Naobranchia occidentalis was found in 
shortraker rockfish from Chirikof, Kodiak, and 
Yakutat in low prevalence (10%) and in rougheye 
rockfish from Yakutat (20%), but not from other ar- 
eas. Prevalence of Chondracanthus pinguis was 
above 40% in Yakutat and Southeast rougheye rock- 
fish, but below 10% in all other samples. This differ- 
ence, however, was a function of size rather than area. 
Prevalence was significantly greater (P=0.069) in 
large rougheye rockfish than in small ones. Colobo- 
matus kyphosus was present in one shortraker rock- 
fish from Yakutat and in two rougheye rockfish from 
Yakutat and Southeast. Chrondracanthus triventri- 
