Spatial and seasonal patterns in the feeding habits of juvenile Lates niloticus (L.), in the Mwanza Gulf of Lake Victoria |
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Authors: | E F B Katunzi W L T Van Densen J H Wanink F Witte |
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Institution: | (1) Tanzania Fisheries Research Institute, P.O. Box 475, Mwanza, Tanzania;(2) Netherlands Institute for Fisheries Research, P.O. Box 68, 1970 AB IJmuiden, The Netherlands;(3) Institute of Biology Leiden, Leiden University, P.O. Box 9516, 2300 RA Leiden, The Netherlands;(4) Koeman en Bijkerk bv, Ecological Research and Consultancy, P.O. Box 14, 9750 AA Haren, The Netherlands |
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Abstract: | Flexibility in the feeding habits of juvenile Nile perch (1–30 cm total length) was studied from September 1988 to September
1989 at four sites (depth range: 1–25 m) in the Mwanza Gulf of Lake Victoria. During this period haplochromine cichlids were
virtually absent in the area. We looked at the combined effects of predator size, season and habitat. Stomach content analysis
showed that with increase in size, the diet of Nile perch shifted from zooplankton and midge larvae, to macro-invertebrates
(shrimps and dragonfly nymphs) and fish. At a size of 3–4 cm Nile perch shifted from size-selective predation on the largest
cyclopoids to predation on the largest, less abundant, calanoids. Zooplanktivory ended at a size of ca. 5 cm. Although an
ontogenetic shift in the diet of juvenile Nile perch was obvious at all sampling stations, the contribution of prey types
appeared to be habitat related. With increasing water depth the frequency of occurrence in the diet of most prey types decreased,
but that of shrimps increased. At the entrance of the gulf (20–25 m deep) shrimps were the main food source throughout the
year. Halfway the gulf (12–16 m), Nile perch showed seasonality in their feeding behaviour. Shrimps were taken there especially
during the rainy season (January to May) when their densities at this station were high, whereas cannibalism prevailed during
the rest of the year. In an environment with Nile perch and dagaa as alternative prey, shrimps were taken almost exclusively.
They could be regarded as a key prey for Nile perch between 5 and 30 cm. |
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Keywords: | dietary shift key prey Nile perch piscivory shrimps |
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