PENNELL, BECKER, and SCOFIELD: HELMINTHS OF KVICHAK SOCKEYE SALMON 



not found. The distribution of these parasites 

 appears to be somewhat sporadic. Data tabu- 

 lated by Margolis (1963) from Bristol Bay sock- 

 eye salmon in 1957 suggest that B. crenatus is 

 more common (40^r incidence) in Kvichak fish 

 than our samples indicate, but concur on the rel- 

 ative scarcity of T. lindbergi and absence of H. 

 levinseni. 



CESTODA 



The tapeworms belonged to five genera and, 

 with the exception of Euhothrium, were either 

 plerocercoid larvae, encysted among the viscera, 

 or sexually immature, postlarval forms in the 

 intestinal lumen. Presumably all infections 

 were acquired by ingestion of cyclopid and/or 

 diaptomid copepods containing infective pro- 

 cercoids. 



Encysted plerocercoids belonging to the genus 

 Diphyllobothrium (Diphyllobothriidae) were 

 fairly common in the stomach walls of many 

 smolts but also occurred, though less frequently, 

 in the liver, spleen, and the intestinal wall. Since 

 the incidence of infection was higher in smolts 

 of age 2 (66%) than in those of age 1 (35%), 

 it appears that the plerocercoids accumulate with 

 continued sojourn of the fish in the lake envi- 

 ronment. The incidence of Diphylloboth7^ium 

 larvae in the viscera of adult sockeye salmon 

 from Pederson Point, which had spent 2 or 3 

 years in the sea, was significantly lower (9- 

 13%). Diphyllobothriasis is common in fresh- 

 water salmonids of the Northern Hemisphere 

 (Becker and Brunson, 1967), but the identities 

 and life cycles of many forms remain unclear. 

 Vik (1964) reviewed the bionomics of Diphyl- 

 lobothrium, and Stunkard (1965) and Meyer 

 (1966) discussed taxonomic problems. Rausch 

 (1954) described the plerocercoids of D. ursi 

 Rausch, 1954, from juvenile and adult sockeye 

 salmon and the adult cestodes from bears on Ko- 

 diak Island, Alaska. Rausch and Hilliard (1970) 

 identified six species of Diphyllohothrium in- 

 digenous in Alaska and noted that several occur 

 as plerocercoids in salmonids and other fresh- 

 water fishes. In all probability, the plerocercoids 

 present in Kvichak sockeye salmon represent two 

 or more species with different definitive hosts 



(birds or mammals) but with otherwise similar 

 life cycles. 



Larvae of Triaenophorus crassus (Triaenoph- 

 oridae) were encysted in either the body cavity 

 or muscle of only four smolts, all of which were 

 age 2. None was detected in returning adults, 

 although apparently the plerocercoids can sur- 

 vive in ocean-dwelling salmon for 4 or 5 years 

 (Margolis, 1963). This cestode is specific for 

 its definitive host, the northern pike (Esox 

 lucius) ; however, the first intermediate host may 

 be one of several species of freshwater copepods 

 (Watson and Lawler, 1965), and the second is 

 a planktivorous fish. Reviews of T. crassus and 

 other species of Triaenophorus were made by 

 Miller (1952), Lawler and Scott (1954), and 

 Michajlow (1962). In the Kvichak system, the 

 incidence of T. crassus in sockeye salmon smolts 

 is apparently low, but it varies among other river 

 systems bordering Bristol Bay (Margolis, 1963, 

 1967) . The fact that Kvichak smolts are largely 

 pelagic apparently accounts, in part, for the low 

 incidence of infection by T. crassus, since cope- 

 pods infected with procercoids will occur most 

 abundantly in shallow, marshy inshore areas in- 

 habited by pike. (Field observations by the sec- 

 ond author in 1958 indicated that the incidence 

 of T. crassus plerocercoids was higher in smolts 

 from Lake Clark, which has a comparatively 

 greater proportion of shoreline to water mass, 

 than in those from Iliamna Lake.) 



Tiny postlarvae of Proteocephalus sp. (Pro- 

 teocephalidae) occurred in the intestinal lumen 

 of about half of the Kvichak smolts, but the in- 

 cidence of infection was lower in age 2 fish 

 (47 % ) than in age 1 ( 62 % ) . Presumably these 

 cestodes had recently emerged after infected 

 copepods were ingested and the smolts were 

 fortuitous hosts in which further development 

 was restricted. The larvae of Proteocephalus in 

 age 2 smolts were no further advanced than those 

 in age 1, and the incidence of infection was lower 

 (47 versus 62%); thus it appears that these 

 cestodes soon perish. No Proteocephalus oc- 

 curred in returning adult sockeye. The favored 

 definitive hosts of this parasite probably are res- 

 ident fish in the Kvichak system. 



Eubothrium sp. (Amphicotylidae), probably 

 E. salvelini Schrank, 1790) on ecological 



271 



