FISHERY BULLETIN: VOL. 71, NO. 1 



the sea. Parasitic infections are considered a 

 possible factor; albeit their effects may be 

 largely sublethal, nevertheless they might con- 

 tribute to disproportionate survival rates. 



A field study of the helminth fauna of sockeye 

 salmon in the Kvichak system was commenced 

 in 1968 and expanded in 1969. The immediate 

 tasks were to (1) identify the parasites acquired 

 in fresh water and those acquired in the sea, (2) 

 determine the incidence and intensity of infec- 

 tions, and (3) review the available literature 

 for information on life cycles. Earlier studies 

 by Margolis (1963) concentrated on parasites 

 of sockeye salmon in the North Pacific Ocean as 

 biological indicators of continental origin; he 

 noted that over 50 parasitic species of fresh- 

 water and marine origin are known to infect 

 sockeye salmon occurring in the North Pacific 

 Ocean and adjacent seas. Many of these para- 

 sites occur in other species of salmon that come 

 from Eurasia and North America to feed and 

 mature in these waters (Akhmerov, 1963; 

 Mamaev, et al., 1959; Mamaev and Oshmarin, 

 1963; Zhukov, 1960). 



MATERIALS AND METHODS 



The Kvichak River system consists of Iliamna 

 Lake and Lake Clark, their tributaries, and the 

 Kvichak River, which leads to the sea (Figure 

 1). Smolts migrate seaward for a few weeks 

 following ice breakup in late May, whereas adults 

 return to spawning grounds in July. Samples 

 were taken from four groups of fish in 1969 

 (Figure 1): 1) smolts, captured by fyke net 

 at Igiugig, on the Kvichak River (Site I), be- 

 tween May 28 and June 6; 2) adults in Bristol 

 Bay, collected by set nets at Pederson Point ( Site 

 II) during May; 3) adults in fresh water, taken 

 by beach seine in the Newhalen River (Site III) 

 during mid-July; and 4) spawners, collected by 

 beach seine on spawning grounds at Finger 

 Beach (Site IV), Woody Island (Site V), and 

 Porcupine Island (Site VI) during August. No 

 attempt was made to discriminate between 

 smolts originating from Iliamna Lake and Lake 

 Clark. Adults collected at Pederson Point in 

 Bristol Bay were known from past tagging ex- 



periments to consist almost entirely of Kvichak 

 sockeye. 



The skin, gills, eyes, gastrointestinal tract, 

 viscera, body cavity, and swim bladder of the 

 fish were examined for helminths. Blood smears 

 were prepared from each fish, gall bladder 

 smears were made from adults, and brain tissue 

 imprints were taken from smolts. Examinations 

 were usually conducted on the day of capture. 

 Thus, most helminths were recovered, tenta- 

 tively identified, and counted while alive and be- 

 fore preservation in hot Formaline-Acetic acid- 

 Alcohol solution (standard solution). In some 

 cases tissues were preserved in hot Bouin's 

 solution (standard solution) for future dissec- 

 tion and examination for parasites. Representa- 

 tive specimens of cestodes and trematodes were 

 stained in Delafield's hematoxylin and mounted 

 for further study; nematodes were either stained 



^ Reference to trade names does not imply endorse- 

 ment by the National Marine Fisheries Service, NOAA. 



Figure 1. — Map of the Kvichak River system, showing 

 sampling sites, with inset map showing its location in 

 southwestern Alaska. 



268 



