Environments occupied, indices of maturity, feeding ecology, shoaling behaviour and interactions with other species by pearl dace, Semotilus margarita (Cope) in Manitoba

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Tallman, Ross Franklin,
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Pearl dace were present only in the headwaters of the Brokenhead River. Males were less abundant than females and the number of males to females decreased from May to November, 1978. Indices of sexual maturity rose steadily from May to November, 1978. From May to August the age classes were separated in horizontal distribution from the youngest (Age 0) in shallow waters to the oldest (Age 2+) in deep waters and the Age 1 dace intermediate between the two. In September and November all ages appeared mainly in pools deeper than 50cm, with the youngest of age groups at the surface and older groups near the bottom. Pearl dace are omnivorous with a diet consisting of insects, insect larvae and other invertebrates, along with plant material and detritus. Much of this material is allochthonous. Overlap of diet between ages was limited. Mouth size differed markedly between age groups. Choice of feeding sites differed among age groups but there was no obvious age dependent difference in feeding times. Interactions with other species were minimized by a lack of dietary overlap and vertical zoning in multispecies schools.