Analyses of stomach contents showed that the kinds of prey eaten by brook trout (Salvelinus fontinalis), cutthroat trout (Salmo clarki), and rainbow trout (Salmo gairdneri) were seldom distributed at random among the individuals. Repeated observation of food eaten by individuals in a stream and ponds showed that prey types were eaten in proportions which were characteristic for an individual.Specialization occurred on several different kinds of prey. Although the degree of specialization was higher during shorter intervals, the data suggested that some specialization persisted for half a year. There were no striking correlations between degree of specialization and other individual properties such as size, growth rate, weight of food, number of food items, previous specialization, or area of recapture.In addition to the observations on trout in relatively undisturbed habitats, a field experiment was conducted using laboratory-reared rainbow trout held in small ponds. The food of each trout in the experiment was sampled repeatedly. In analysis of variance, interaction among the individuals and kinds of prey eaten showed that food specialization occurred. Both the absolute and relative abundance of potential prey were constant during the experiment.

Feeding history and parental stock were manipulated to determine whether they could influence food selection in young trout, Salmo gairdrceri Richardson. After 9 training meals of one food, trout selected that food, the familiar one, when given a choice between it and a novel food. (Most choice situations used high and equal densities of unconcealed foods). Selection of the familiar food occurred with several kinds of non-living food. Trout trained on live prey, however, did not always select the familiar one when botli prey were alive, although they did when both prey were dead. Some characteristics of the training effect were investigated. As they became satiated, trout consumed relatively more of the novel food. Duration of food deprivation before a choice test did not change the degree of selection for the familiar food. In addition to eating more of the familiar food, trout struck but rejected relatively more of the novel food. Individual trout trained on two foods ate them in proportions which were characteristic for an individual. After they had learned to select one food, trout were given further training on one of the following: the familiar food, a novel food, or both. Further training on the familiar food did not change the proportion selected. Trout trained on one food for 12 meals and then on a second food for 12 meals selected the second food when given a choice. When the initial training was followed by continuous feeding of both familiar and novel food, trout continued to select the familiar food for 14 to 23 meals. All results suggested that effects of such feeding history would not greatly influence food selection in natural situations. Progeny of different parental stocks were tested to determine whether parental food can influence food selected by offspring. Eggs from trout which ate different kinds of food were hatched in the laboratory. For their first meal, trout were given choices of the kinds of food eaten by the parental stocks. In three main experiments, the young trout did not select the type of food commonly eaten by their parents.

Arctic grayling, Thymallus arcticus, and Arctic char, Salvelinus alpinus, were collected by angling and seining in remote areas of northern Yukon Territory. Stomach samples were observed to test the hypothesis that fish caught by angling had eaten less food than those caught by seining. The hypothesis was supported by the data for grayling. The data for char were consistent with the hypothesis, but the results were not statistically significant. There was no difference in the sex ratio of fish caught by the two methods. Angling selected larger char than did seining, but there was no evidence of size selection in grayling.

Spawning grounds used by lake (Coregonus clupeaformis) and round whitefish (Prosopium cylindraceum) were discovered in the course of an investigation on effects of hydroelectric development. The spawning period for lake whitefish extended from early November to at least mid-December 1973. Lake whitefish spawned over silt and Potomogeton in water which had little current and was 2.0–2.5 m deep. Spawning of round whitefish was probably completed in November. Round whitefish spawned during the day. Eggs were apparently broadcast over a variety of substrata ranging from silt and Potamogeton to gravel and boulder. Round whitefish eggs were deposited in both fast and slow current at depths ranging from 0.7 to 2.5 m. Although deposited in a range of habitats, round whitefish eggs seemed to be most abundant on gravel in fast current at depths less than 1 m.

No abstract