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A comparative study of the behaviour of two sympatric species of freshwater sculpins, Cottus asper Richardson and Cottus aleuticus Gilbert, in relation to their differences in microhabitat Fenwick, Julie M.


The behaviour of two sympatric species of sculpins, Cottus asper and Cottus aleuticus, which occupy different microhabi-tats, was studied by the comparative method. The aim of the study was to determine some of the important behavioural adaptations to the differences in their microhabitats. C. asper occurs in areas of slow current and fine substrate and G. aleuticus in areas of fast current and coarse substrate. The posture, orientation to the current, and locomotary and feeding behaviour of the species were examined in the laboratory under different conditions of current and substrate. C. asper responds to a current by lying flat on the substrate. C. aleuticus also exhibits this posture on sand, but on a gravel substrate, raises the body, by spreading the pectoral fins. C. aleuticus adopts a parallel orientation to the current more frequently than a broadside orientation, but C. asper "prefers" the broadside position. However, both species assume the broadside position more frequently on sand than on gravel, and the parallel orientation more frequently on gravel than on sand. C. asper is a much poorer swimmer than C. aleuticus, especially in a current. C. aleuticus is much more active than C. asper at all times of day and under all conditions of current tested. C. asper is a lurking predator and takes food from the surface of the substrate. C. aleuticus is a more active feeder, and feeds by swimming to the water surface, by taking food from the substrate surface and by foraging in the crevices of the gravel. From laboratory observations it appears that C. aleuticus relies on sight in food detection to a greater extent than does C. asper. The findings of this study were compared with field observations and with previous studies of other cottid species. It was concluded from this that C. aleuticus’ posture, orientation to the current, and locomotory and feeding behaviour are a reflection of a more active way of life and are related to the special problems of life in a strong current. C. asper, however, is typical, both in behaviour and morphology, of bottom-dwelling, sedentary fish, of reclusive habits.

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