The life cycle of Phflonema oncorhynchi was studied in sockeye salmon, Oncorhynchus nerka, from Cultus Lake, British Columbia. Gravid female worms from the coelom of sockeye spawners burst in lake water releasing living first-stage larvae. These were ingested by Cyclops bicuspidatus and developed to the infective third stage in the haemocoele. Development required 17 days at 12 C or 70 days at 8 C. Each of six hatchery-reared sockeye fingerlings were fed 14-70 copepods infected with third-stage larvae. Fourth-stage larvae were recovered from the peritoneal tissues of four fingerlings when examined four to ten days after infection. The later stages of development were studied by maintaining naturally infected sockeye salmon for two years in freshwater. These had early fourth-stage larvae in the parietal peritoneum and tunica adventitia of the swim bladder when captured as downstream migrants at Cultus Lake. When the fish were 26 months old, late fourth-stage larvae were found in the peritoneal tissues. These moved into the coelom when the fish were 32 months old and moulted to the preadult stage. The comparative morphology of mature worms collected from B.C. salmonids was studied. The type species, Philonema oncorhynchi Kuitunen-Ekbaum, 1933 was obtained from the type host, Oncorhynchus nerka, in the type locality, Vancouver, B.C. Philonema were also obtained from salmonids with a freshwater life cycle in a landlocked area, Kootenay Lake, which was once contiguous with the type locality of Philonema agubernaculum Simon and Simon, 1936. The morphology was constant for worms found in different hosts and geographical areas. Size was an unreliable characteristic and appeared to be a host-dependent variation. The type specimens of Philonema agubernaculum Simon and Simon, 1936 were examined and no differences in morphology found. / Science, Faculty of / Zoology, Department of / Graduate

This study was undertaken to determine the identity of Philonema oncorhynchi from anadromous sockeye and Philonema agubernaculum from non-anadromous trout, and also to test the hypothesis that the worm in salmon is dependent on hormonal stimulus from the host for synchronization of reproduction. On the basis of differences found in life cycles, cross infection and starch gel electrophoresis, P. oncorhynchi and P. agubernaculum are considered to be different species. The hypothesis was tested experimentally, using salmon pituitary extracts and synthetic stilbestrol. Pituitary extracts accelerated the production of larvae in the uterus, of the worm and stilbestrol inhibited the gonadal development of the fish, but had no apparent effect on the worms. The hypothesis was further supported by the results of transplantation of adult but non-larvigerous worms from maturing sockeye into immature trout. Larval development failed to take place in recipient hosts. As well, larvigerous worms were collected only from sexually mature fish, whether 3, 4 or 5 years old. Rapid development of the worm paralleled the rapid gonadal development of the fish during the last 6 months of the fish's life. Sexually immature sockeye had only immature worms. / Science, Faculty of / Zoology, Department of / Graduate

Development of Philonema oncorhynchi and Philonema agubernaculum in Cyclops bicuspidatus were followed and compared by experimentally infecting the copepods with larvae obtained from gravid female worms in spawning salmon and trout. Larvae were dissected from copepods for examination at an interval of two to three days. They were found to undergo two moults in the copepods. Three larval stages are described. All the larval stages of the two species of Philonema are morphologically identical. The rates of development of the larvae were observed to be directly proportional to temperatures between 4° to 15°C. The Q₁₀ for the range was calculated as 4. The rates of development at 10° were the same in the two species. The effects of temperature on larval development are discussed. An attempt is made to correlate the rates of development of Philonema larvae in the copepods under laboratory conditions and the infection of sockeye salmon in Cultus Lake, British Columbia. / Science, Faculty of / Zoology, Department of / Graduate