Intraspecific patterns of resource use by fathead minnows in a small boreal lake

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Abstract
An isolated, single-species assemblage of fathead minnows (Pimephales promelas) was studied to identify patterns of feeding and diel activity among three life-history groups (adult males, adult females, and juveniles). Minnows were collected from inshore and offshore stations during monthly (May–August) 24-h sampling periods. Minnows appeared flexible in their choice of food items, concentrating their feeding on invertebrate taxa, such as emerging chironomid pupae, that were temporarily available, as well as on relatively large and vulnerable microcrustaceans, such as Daphnia. Adult males, larger than females and juveniles, consumed the amphipod Hyallela azteca to a greater extent than the two smaller-bodied groups. Patterns of habitat use and activity were also consistent with behavioral flexibility. Prior to the breeding season, when all three groups were abundant, the population displayed intraspecific differences in diel activity; adults were typically active at night, when chironomid pupae were most abundant, whereas juveniles were primarily day active. Later, as catches of males declined, spatial and temporal patterns of females and juveniles were similar and diet overlap was high. Characteristics of both the fish population and their prey interact to shape patterns of resource use in fathead minnows.

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