Some remarks on the occurrence and development of philometrid nematodes infecting the white sucker, Catostomus commersoni Lacépède (Pisces: Catostomidae), in Ontario

During a study on the parasitofauna of white sucker (Catostomus commersoni) in Laurel Creek, Ontario, three philometrid nematodes were found. Gravid and subgravid females completing the life cycle occurred very infrequently (Philometroides huronensis: 4.3%, Philometroides nodulosa: 1.6%, Philometra kobuleji: 1.1%). In comparison, males and retarded females infected the eyeball and the peritoneum around the swim bladder very often (43.1 and 31.6% in total, respectively). Less frequently, developmental stages were found in the abdominal cavity. Specimens found in the eyeball were identified as belonging to P. nodulosa, while the swim bladder forms could belong to P. huronensis or to P. kobuleji. The eyeball and the peritoneum around the swim bladder are regarded as refuges for retarded forms, where they can survive for more than a year. No evidence was found of a direct cause of retardation.

Benthic Fauna Colonization of a New Reservoir with Particular Reference to the Chironomidae

At the time of first filling of Laurel Creek Reservoir in the spring of 1967 the benthic fauna consisted of submerged terrestrial organisms and obligate and facultative rheophilic species. Two months after initial filling substantial populations of colonizing limnophilic species developed in the habitat whereas the terrestrial and obligate rheophilic components were lost. By the 4th month the fauna was dominated by euryoxybiontic limnophiles and by facultative species. In the period immediately prior to reservoir drainage in the autumn of 1967 the population densities of the euryoxybiontic chironomids declined whereas polyoxybiontic species continued to increase in abundance. These changes in the dominance hierarchy of the chironomid fauna were associated with the partial loss of the rich deposits of organic debris by siltation and decomposition. Survival of winter drainage of the reservoir by many limnophilic species produced an appreciably different pattern of colonization when the reservoir refilled in 1968. During the second summer of the reservoir's existence most euryoxybiontic chironomids further declined in abundance and were replaced by polyoxybiontic forms as the dominant species. The facultative species originally derived from the creek fauna are adapted to a wide range of environmental conditions and the modifications of the reservoir habitat with time had little effect on their abundance.

Macroinvertebrate colonization of the marginal zone of a small impoundment in Eastern Canada

Colonization of the marginal macroinvertebrate fauna of Laurel Creek Reservoir was followed from the time of first filling in the spring of 1967 until the reservoir was drained in mid-October of the same year. Of the 55 taxa found during this period 34 (61.8%) were facultative species which had maintained populations in the lotic environment before impoundment. Colonization was an active process which accelerated as the water temperature increased. Passive colonization by species swept into the reservoir by flooding of the creek and the resultant rapid filling of the reservoir was negligible. For the first 3 months after subsequent filling in the spring of 1968 the marginal fauna was very similar to that of the previous year although colonization was more rapid as a result of overwintering of many limnophilic species in various refugia in the reservoir basin. Colonization of the marginal zone appeared to approach completion, with respect to the prevailing environmental conditions, during the first summer period of the reservoir's existence.