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A system to designate and define isolates of Trichinella spiralis is proposed. The designation gives the host from which the isolate was recovered, geographic origin, and year of recovery. Isolates of T. spiralis recovered from frozen muscles from four species of wild carnivores had low and different infectivity to laboratory mice. Viable larvae of T. spiralis were obtained from muscle samples of marten, wolverine, polar bear and arctic fox which had been frozen for 5, 6, 12 and 14 mo, respectively.

Larvae of the nematode Raphidascaris acus were found free or encapsulated in the liver of yellow perch. Blood vessels were distorted or destroyed during larval migrations and larvae were eventually encapsulated in a thick-walled whitish nodule. Successful walling-off of the parasite resulted in the formation of a collagenous nodule and a complete loss of the worm. No mortality of perch was associated with larval R. acus but the introduction of susceptible fishes into a lake harboring this parasite may be important in some stocking programs.

Samples of muscle from 4,773 specimens of 18 species of wild mammals from Ontario were examined for Trichinella. One of 12 mink (Mustela vison), 83 of 1,821 fisher (Martes pennanti) and 68 of 1,980 marten (Martes americana) had T. spiralis. Prevalences of infections by Trichinella were determined for fisher and marten from the Algonquin region, over a 10-yr period. Prevalences ranged from 0.9-9.2% in fisher and 1.3-8.7% in marten indicating that the parasite is well-established in the region. Prevalences of Trichinella increased with age of both fisher and marten. Intensities determined for the 1981-1982 sample ranged from 0.4-15.8 larvae/g for fisher and 22.4-159.7 larvae/g for marten. Higher intensities were not correlated with older hosts. Fisher and marten appeared to be the key hosts maintaining Trichinella in the Algonquin region, but transmission dynamics were unclear. Transmission may include an unidentified small rodent or other host and natural carrion-feeding.

Rainbow trout (Salmo gairdneri) stocked into a small prairie dug-out were examined for helminths at harvest time. Five species of helminths were found (Diplostomum sp., Diplostomulum scheuringi, Clinostomum complanatum, Crepidostomum farionis and Pomphorhynchus bulbocolli); C. farionis and P. bulbocolli mature in fish while the remaining species utilize fish-eating birds as definitive hosts. Examination of stomach contents indicated that all invertebrate hosts required for the life-cycles of these helminths were present in the dug-out. The most conspicuous and prevalent helminth was C. complanatum as fish were "wormy" and unmarketable due to the presence of high numbers of metacercariae. Metacercariae of C. complanatum were recovered from most organs of rainbow trout. The low survival of stocked fish suggests that C. complanatum may cause some host mortality, but the condition of infected and uninfected fish was similar. It appears that a community of ichthyoparasites can become established in a population of stocked fish in a single growing season in north temperate regions.

Six species of parasites were recovered 4 mo after walleye fry were stocked in Heming Lake, Manitoba. The species of parasites acquired most rapidly were those that were non-host-specific and common to the indigenous populations of both walleye and yellow perch (Perca flavescens). Parasite species overlap (Jaccard's indices) was greatest within age groups of walleye and yellow perch, but was also high between older walleye and yellow perch. The higher numbers of parasites recruited by stocked walleye, particularly ones known to induce pathology, raises questions on the success of walleye introductions to aquatic systems with a diverse indigenous parasite fauna and a fish population with a large proportion of yellow perch.

Seven species of helminths were recovered during a survey of 162 fisher (Martes pennanti) from four areas of Manitoba: Baylisascaris devosi in 52 fisher; Taenia sibirica in 25; Physaloptera sp. in nine; Alaria mustelae in two; Metorchis conjunctus in one; Trichinella spiralis in one of 81; Molineus sp. in one. B. devosi was the most prevalent parasite and differences in its geographical distribution were possibly related to population density of fisher. The prevalence of other parasites did not appear to be related to density of fisher.

The objectives of this study were to determine if the raccoon was a useful experimental animal for infections of Trichinella and to determine if the ability of Trichinella to survive freezing conditions, known to occur in wild animals, could be duplicated under laboratory conditions. The isolates of Trichinella used in this study were from pigs, polar bear, wolverine, arctic fox and T. spiralis var. pseudospiralis originally isolated from a raccoon in the USSR. The raccoon was found to be a useful experimental host for Trichinella as it was easily maintained under experimental conditions and was readily infected. Infectivity indices were lower in raccoons than in laboratory mice. Those isolates of Trichinella with the longest association with laboratory mice had the lowest infectivity indices. The isolate of Trichinella from an arctic fox retained its ability to survive freezing temperatures when introduced into raccoons held under experimental conditions. The type of host, method of passing the parasite and perhaps a special genetic characteristic of arctic isolates seem to be important factors influencing their ability to survive freezing temperatures.

This study concerned the suitability of rainbow trout as an experimental host for plerocercoids of Triaenophorus crassus. Twenty-five trout were exposed to Cyclops bicuspidatus thomasi infected with procercoids of T. crassus. Plerocercoids were recovered from 11 of these fish. Hemorrhaging in the muscle was the first evidence of infection in live fish between Days 22-58 postinfection (PI). Migration of worms created extensive lesions in the muscle by Day 30 PI followed by formation of granulomas between Days 45-75 PI. One to three plerocercoids were wound throughout the muscle after Day 30 PI, and penetration into the body cavity and through the integument was common. Mortality of infected trout was first observed at Day 44 PI, and by Day 56 PI, 45% of the trout died. The swimming behavior of infected trout was marked by decreased activity and loss of equilibrium.

A stocking program with rainbow trout (Salmo gairdneri) at High Rock Lake, Manitoba failed due to infections with large numbers of Contracaecum spp. larvae. Nematode larvae in the intestinal tract, body cavity and musculature made the fish unmarketable. A combination of experimental infections of rainbow trout and pelicans (Pelecanus erythrorhynchos), observations on the behavior of fish-eating birds, and numbers of larval Contracaecum spp. in minnow species led to the following conclusions. The introduction of rainbow trout attracted large numbers of fish-eating birds, particularly pelicans. Concurrent predation by rainbow trout on fathead minnows (Pimephales promelas), five-spined sticklebacks (Culaea inconstans), and nine-spined sticklebacks (Pungitius pungitius), concentrated the parasites. The combined increase in densities of the introduced fish host and fish-eating birds, and the short life cycle of the parasite, increased the numbers of parasites in rainbow trout over a season and in the indigenous minnow species between years. Numbers of larvae in the indigenous minnow species declined when stocking of rainbow trout was stopped and use of the lake by fish-eating birds, particularly pelicans, returned to normal levels.

Seven species of ectoparasites were recovered during a survey of sharp-tailed grouse, Pediocetes phasianellus, including the ticks, Haemaphysalis chordeilis and H. leporispalustris; the lice, Goniodes nebraskensis, Lagopoecus gibsoni and Amyrsidea sp.; the hippoboscid fly, Ornithomyia anchineuria; and the mite, Ornithonyssus sylviarum. Seasonal changes in populations of ticks and lice were found but not for populations of the hippoboscids or mites. All stages of H. Chordeilis were found on sharp-tailed grouse only. Larvae and nymphs of H. leporispalustris were found on sharp-tailed grouse and song birds. Larvae, nymphs and adults of H. leporispalustris were recovered from a snowshoe hare. Small mammals from the study area did not harbour any species of ticks.

Five species of helminths were recovered during a survey of 139 North American pine marten (Martes americana) from three areas of Manitoba: Alaria taxideae in 75 marten; Taenia sp. (cf. martis martis) in 16; Taenia mustelae in nine; Baylisascaris devosi in one; Trichinella sp. larvae in one. Taenia mustelae and Taenia sp. (cf. martis martis) were found in two different areas of the province, Taenia sp. (cf. martis martis) being isolated from the more northerly regions. Alaria taxideae, the most prevalent parasite in the survey, was common to all three areas. The intensity of infection and prevalence level of A. taxideae was significantly higher (P less than 0.05) in the southern region of this study. Altogether, male marten had a significantly higher intensity of A. taxideae compared to females, although there was no significant difference in prevalence level. When data for A. taxideae was combined for sexes and for regions a significantly higher prevalence level in young-of-the-year marten was noted compared to juveniles or adults, but no significant difference in intensities among the three age classes was found. No significant differences were detected in the prevalence of A. taxideae, Taenia sp. (cf. martis martis), or T. mustelae between sexes or among age classes from any of the three areas.

Ninety-five percent of the larvae of Contracaecum spp. were found in the atrium of the heart of fathead minnows (Pimephales promelas) and five- and nine-spined sticklebacks (Culaea inconstans and Pungitius pungitius). Atria containing nematodes were two to three times larger than an atria from uninfected fish, were thin walled and the muscular trabeculae were damaged. Atria with larvae were congested with blood that appeared to be organizing and extending as a thrombus into the ventricle, but there was no other evidence of a host response. Alternatively, there was an intense cellular response surrounding larvae in the body cavity of these and other host species. Apparently, this parasite which lacks host specificity has evolved an additional strategy to evade the host immune response in sticklebacks and fathead minnows.