FISHERY BULLETIN: VOL. 71, NO. I 



grounds, occurred as adults in the intestines of 

 three smolts. This holarctic cestode appears to 

 be rare in sockeye salmon in major Bristol Bay 

 watersheds (Margolis, 1963, tables) but is some- 

 times common in salmonids from other areas. 

 Infections of about 35% incidence occurred in 

 sockeye smolts leaving Babine Lake, British Co- 

 lumbia, in 1952 and 1953 (Dombroski, 1955) , and 

 an incidence of 20-30% among these migrants 

 has been recorded recently (Smith and Margolis, 

 1970). There is no teleost intermediate host 

 for Eubothrium, and juvenile sockeye salmon 

 become infected directly by ingestion of plank- 

 tonic copepods carrying procercoids, such as 

 Cyclops strenuus in Norway (Vik, 1963). E. 

 salvelini apparently does not survive the sojourn 

 of growing sockeye salmon at sea. Recent evi- 

 dence suggests that cestodes of a related species, 

 Eubothrium crassum (Bloch, 1779), found in 

 returning Atlantic and Pacific salmon in rivers, 

 are rarely the same worms carried to sea by 

 smolts but are of marine origin, and that two 

 biological races, one marine and one fresh water, 

 exist (Kennedy, 1969). 



Postlarval forms of Phyllobothrium caudatum 

 (Tetraphyllidea) were found in the digestive 

 tract of all fish taken at Pederson Point, the New- 

 halen River, and the spawning grounds (mean 

 intensity, 16/fish). Little decrease was appar- 

 ent in either incidence or intensity of infection 

 in adults that reached fresh water despite their 

 cessation of feeding. The unencysted postlarvae 

 exist in a state of arrested development. They 

 live in captive juvenile pink and chum salmon 

 in seawater for at least 8 months with no change 

 in form, but grow from 1 to 4 or 5 mm (Boyce, 

 1969). Moderate to heavy infections of phyl- 

 lobothriids are acquired by nearly all species of 

 salmon feeding in the North Pacific (Akhmerov, 

 1963; Margolis, 1963; Zhukov, 1960) and their 

 numbers are apparently cumulative. The ma- 

 ture form and the definitive host of this cestode 

 remain unknown, and some taxonomic confusion 

 exists as to its specific identity. Williams 

 (1968), who reviewed the Phyllobothriidae, con- 

 curred with Margolis (1963) in identifying the 

 postlarvae from sockeye salmon in the North 

 Pacific and adjacent seas as P. caudatum. The 

 hosts of larval Phyllobothrium include marine 



cephalopods, elasmobranchs, teleosts, and mam- 

 mals, but the mode of infection and subsequent 

 behavior of the late procercoid and developing 

 plerocercoid are not known (Williams, 1968). 



ACANTHOCEPHALA 



The incidence of Neoechinorhynchus rutili 

 (Neoechinorhynchidae) among the smolts was 

 low and tended to be greater among those of 

 age 2 (13%) than those of age 1 (2%). None 

 was found in returning adult sockeye. Tabu- 

 lated data by Margolis (1963) indicate that this 

 acanthocephalan does not survive the sockeye's 

 ocean residence. A^. rutili developed rapidly, 

 and hence the parasites carried in the intestine 

 of smolts were sexually mature. Margolis 

 (1963) listed an incidence of 8% in Kvichak 

 smolts examined in 1956. 



A^. rutili is an euryxenous parasite with wide 

 dispersal in freshwater habitats of Eurasia and 

 North America (Van Cleave and Lynch, 1950) 

 and is the only species of the genus found in 

 European freshwater fishes (Bullock, 1970). 

 The only known intermediate host of N. rutili 

 in North America is the ostracod Cypria turneri 

 (Merritt and Pratt, 1964), whereas in Great 

 Britain there are two known intermediate hosts, 

 the ostracods Cypria ophthalmica and Candona 

 Candida (Walker, 1967). The ostracod Cyclocy- 

 pris laevis and two species of Sialis (Insecta) 

 are known to transmit the infective larvae to fish 

 in Europe (Ginetsinskaya, 1958). 



Echinorhynchus gadi (Echinorhynchidae) oc- 

 curred in six adult sockeye salmon from Peder- 

 son Point. According to Margolis (1965), this 

 acanthocephalan is widely distributed in north- 

 ern seas; it is common in sockeye salmon taken 

 off the Kamchatka Peninsula of the USSR but 

 is generally rare in salmon captured in other 

 areas, including the North American coast. E. 

 gadi, like N. rutili, is an euryxenous parasite but 

 differs in that it originates in the sea. It occurs 

 in many families and genera of teleosts in the 

 North Pacific and North Atlantic, particularly 

 demersal fishes, but most commonly in the cods 

 (Gadidae) (Linton, 1933; Margolis, 1965; Sin- 

 dermann, 1966). The first intermediate hosts 

 are marine amphipods, such as Gammaru^ lo- 



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