FISHERY BULLETIN: VOL. 71, NO. 4 



labis were much larger than males and occurred 

 less frequently (Table 4). The range of trunk 

 lengths for both males and females is increased 

 from the original reporting — females 18.0 to 

 26.7 mm, now 13.5 to 35.0 mm, and males 9.20 

 to 12.16 mm, now 7.5 to 14.0 mm. All females 

 with trunk lengths exceeding 15.0 mm were 

 swollen with bipolar eggs. 



Occurrence of this parasite as presented in 

 Tables 1 and 4 was minimal since worms were 

 often squeezed from the host's anus as fish were 

 brailed aboard the ship. Occurrence of R. colo- 

 labis showed inconsistent geographic and 

 annual variability precluding further meaning- 

 ful analysis. Proportions of infected saury in 

 1970 samples ranged between 70.0 and 90.0% 

 (mean 78.0% ) off Oregon and between 40.0 and 

 55.0% (mean 48.3% ) off Washington. Like the 

 parasitic copepods, incidence of infection was 

 generally lower in 1971, ranging between and 

 15.0% (mean 7.5% ) off Oregon and between 45.0 

 and 89.5% (mean 67.2%) off Washington. Rates 

 of infection were found to be independent of 

 host size and age. 



R. coiolab/s in Steelhead Trout 



The steelhead trout was found bearing the 

 adult form of the same acanthocephalan identified 

 in Pacific saury. Steelhead trout had previously 

 been reported with an acanthocephalan 



identified as Rhadlii(>rhy)ichH.'^ sp., Shaw (1947); 

 however, more recent or specific reports have 

 not been located. 



C. M. Senger, Professor of Biology, Western 

 Washington State College, Bellingham, Wash., 

 recovered two Acanthocephala from steelhead 

 trout captured in Skagit County, Wash., in 

 1967-68. He later compared these with specimens 

 I supplied from Pacific saury and concluded 

 both hosts carried R. cololabis. Additional 

 steelhead trout from Skagit County (1969-72) 

 and from high -seas areas of the northwestern 

 Gulf of Alaska (August 1970) were subsequently 

 examined. Nine of 28 steelhead trout from 

 Skagit County and 4 of 22 steelhead trout from 

 the northwestern Gulf of Alaska were infected 

 with R. cololabis. Multiple but not severe in- 

 fections were noted from hosts collected in 

 both areas. The heavy egg load carried by 

 female R. cololabis indicated the steelhead 

 trout to be a second definitive host. 



Copepod Infections in Two Possible 

 Subpopulations of Saury 



Chi-square analysis was applied to test the 

 null hypothesis that no significant differences 

 (0.05 level) in numbers of infected fish existed 

 between the two possible subpopulations (spring- 

 and autumn-born saury) that were classified 

 bv means of scale features. The two indicators 



Table 4. — Intensity of infection, sex ratio, and trunk length of RhuiUnorhynchiis cololabis from Pacific saury captured off 



the Pacific coast of North America during August -September 1970-71. 



Trunk length (mm) 



17.0 

 21.0 



23.8 

 20.3 



950 



