372 
Fishery Bulletin 99(2) 
178° 176° 174° 172° 170° 168° 166° 164° 162° 160° 158° 156° 154° 152° 
Location of trawl hauls in the Gulf of Alaska and Aleutian Islands where northern and southern rock sole were 
examined for gill parasites. 
Materials and methods 
Between 8 and 18 June 1996 (Table 1), northern and 
southern rock soles captured in a series of trawl hauls 
from the western Gulf of Alaska were examined for para- 
sites (Fig. 1). Between 25 and 27 June 1997 (Table 1), we 
examined northern rock soles from a series of trawl hauls 
around Seguam Island and the east end of Amlia Island 
in the central Aleutian Islands. The two sampling areas 
are approximately 850 km apart. We scanned the interior 
and exterior surfaces of gill filaments on all gill arches 
for parasites. All rock soles were examined in hauls with 
few fish (n<50), and a random selection of fish in larger 
hauls were subsampled in a manner similar to that used 
for obtaining a random subsample for lengths (see Martin, 
1997, for Gulf of Alaska bottom trawl survey methods). For 
each parasitized fish, we measured the fork length (FL) in 
centimeters, weight (±2 grams), determined the sex, and 
removed and froze the entire head, including gill arches, 
at sea. Lengths and weights were also collected from unin- 
fested northern and southern rock soles in the Gulf of 
Alaska survey for comparisons with parasitized fish. 
Frozen heads were thawed slowly in a refrigerator; thaw- 
ing heads quickly in warm water produced gill filaments 
with an excess of mucus, making it difficult to locate para- 
sites. Host species identification was confirmed by examin- 
ing the gill rakers on the first gill arch on the blind side, and 
by counting supraorbital pores (Orr and Matarese, 2000). 
The internal and external surfaces of all gill filaments were 
examined for parasites with a dissecting microscope. The 
parasites were removed from gill filaments by washing with 
water into a filter, or pulling with tweezers, or by removing 
the gill filament if the parasite was well-anchored. All par- 
asites were preserved in 10% formalin for 3-5 days and 
stored in 70% ethanol with a small amount of glycerol (Ka- 
bata and Cousens, 1972). Fish heads were fixed in 10% for- 
malin for up to one week and stored in 70% ethanol. 
We identified the parasites by using the key of Kabata 
(1988), and Kabata verified our identifications. Generally, 
only female parasites, which measured at least 2 millime- 
ters in length, were enumerated. Males were found occa- 
sionally, sometimes attached to females. However, males 
were too small (<0.3 mm in length) to identify and quanti- 
fy; therefore males were not included in any summaries or 
