FISHERY BULLETIN: VOL, 71, NO. 1 



es. Anadromous salmonids carry the parasites 

 into fresh water. Nearly all adult sockeye salm- 

 on taken at Pederson Point harbored quantities 

 of larval anisakids belonging to these two re- 

 lated genera. Accurate records of adults infect- 

 ed with either Contracaecum and/or Anisakis 

 were not obtained, but the actual combined inci- 

 dence was probably 100 % , as tabulated for Bris- 

 tol Bay sockeye salmon returning in 1957 by 

 Margolis (1963). In our study, these helminths 

 were listed simply as nematodes because of the 

 difficulty of individually examining large num- 

 bers of parasites scattered throughout the vis- 

 cera of the large fish. On the basis of preserved 

 material from adult sockeye salmon taken at 

 Pederson Point, the ratio of P. oncorhynchi to 

 Anisakis to Contracaecum was about 1:2: 1.5 by 

 total numbers. 



According to Margolis (1970), the typical life 

 cycle of nematodes belonging to the superfamily 

 Ascaridoidea (including all anisakids) occurring 

 in fishes probably involves three hosts — a crus- 

 tacean or other invertebrate as first intermediate 

 host, a fish as second intermediate host, and a 

 piscivorous fish, bird, or mammal as the defin- 

 itive host — depending on the genus or species 

 concerned. Whether the larval Contracaecum 

 found in Kvichak smolts in this study are iden- 

 tical with those in returning adult sockeye salm- 

 on is problematical, but it is possible that stages 

 liberated from spawning fish were acquired by 

 some smolts. 



INTENSITIES OF FRESHWATER 

 HELMINTHS IN SMOLTS 



Ten helminths with life cycles involving ini- 

 tial transfers in the freshwater environs were 

 harbored by migrating Kvichak smolts (Table 

 1). One of the objectives of this study was a 

 determination of the potential eflfects of these 

 helminths, however subtle and indirect they may 

 be. Some indication is provided by the intensity 

 of infections in correlation with the site selected 

 for latent or active development. 



Ecologically speaking, the intensity of infec- 

 tion is roughly correlated with the incidence of 

 infection because the more abundant the para- 

 site, the greater will be the distribution of in- 



fections among all available hosts. Moreover, 

 the higher the incidence and/or intensity of in- 

 fection, the more favorable will be the sum of 

 all synecological factors involved in sustaining 

 a particular host-parasite association. 



The intensities of the five common helminths 

 acquired by smolts in Iliamna Lake and Lake 

 Clark are given in Table 2. Accurate counts 

 were not made of the ubiquitous Philonema on- 

 corhynchi and data on the adventitious Proteo- 

 cephahis sp. are omitted. Some additional data 

 are included from smolts captured in previous 

 years, preserved in Formalin, and subsequently 

 examined. Of these helminths four occurred as 

 immature or larval forms in the body cavity, tis- 

 sues, or organs. 



The acanthocephalan Neoechinorhynchus ru- 

 tili inhabits only the intestine of smolts, where 

 it rapidly matures. In this favored location the 

 female releases the eggs, these are passed ex- 

 ternally, and the worms eventually degenerate. 

 Infection burdens were found to be low in this 

 study, with usually one but sometimes two par- 

 asites per host. With such low intensities, fertil- 

 ization of eggs in the intestine (which requires 

 association of a male and a female) is excep- 

 tional and the parasite tends to be self-limiting. 

 Consequently, the principal definitive hosts in 

 the Kvichak system are probably resident fishes 

 that sustain an infection foci. The data, though 

 scanty, suggest that infection of smolts occurs 

 primarily in Iliamna Lake since samples from 

 Lake Clark and its tributary, the Newhalem Riv- 

 er, harbored none. Data presented by Margolis 

 (1963) for 25 Kvichak smolts in 1956 list an 

 incidence of 89f and a mean intensity of one 

 parasite per fish. 



Diplostomulum sp., Diphyllobothrium spp., 

 and Triaenophorus crassus persist in sockeye 

 salmon as larvae throughout the life of their 

 host. Completion of their life cycles requires 

 that an infected fish be eaten by a predator or 

 scavenger in which the parasite is able to mature 

 and shed its eggs. Philonema oncorhynchi trans- 

 forms from larvae to adult in sockeye and is lib- 

 erated during the spawning act or upon the host's 

 death. 



Both the incidence and intensity of Triaenoph- 

 orus crassus were low in Kvichak smolts in this 



274 



