Diet changes in prey size selectivity in larvae of perch <Emphasis Type="Italic">Perca fluviatilis</Emphasis> |
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Authors: | V N Mikheev J Wanzenböck |
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Institution: | (1) Department of Biological and Environmental Sciences/Aquatic Sciences, University of Helsinki, P.O. Box 65, FI-00014 University of Helsinki, Finland |
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Abstract: | A hypothesis on change in prey size selectivity in relation to illumination level was tested on the basis of data on weight
and size composition of the content of the digestive tract of larvae of perch Perca fluviatilis and on zooplankton in the layer 0–6 m (Wallersee Lake, Austria). Larvae foraging in the twilight-night period had almost
two times more food in the intestine than those foraging in the daytime. The size composition of perch larvae and concentration
and size composition of zooplankton hardly differed in the daytime and twilight-night samples. For the first time, it is shown
on field material that more intensive feeding of larvae at twilight is related to selection of significantly larger prey than
in daytime feeding. In the day-time, the larvae consumed more prey but their maximum size did not exceed 0.6 of the diameter
of mouth opening of the fish; at twilight it was over 0.8. In case of feeding on so large prey, not only the weight of the
consumed feed increases but the time used for capture and swallowing also considerably increases. The larvae which in the
period of investigation did not yet form schools, which perform the principal defensive function, were especially vulnerable
for predators feeding on relatively large prey. The decrease of the part of small-sized prey at twilight is not related to
their lesser availability due to a low illumination. It is assumed that feeding on energetically more valuable but less available
prey is shifted to the period of low illumination when the larvae are less exposed to predation risk. The obtained results
are discussed from positions of the triotroph concept (Manteifel’, 1961). |
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