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Dietary preference of nile tilapia versus native fish species in the upper Kabompo River, northwest of Zambia

Arthertone Jere*, Wilson W. L. Jere, Austin Mtethiwa, Daud Kassam

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ABSTRACT: Understanding the dietary preference of fishes is fundamental in fisheries and conservation biology research. In this study, dietary preference of Oreochromis niloticus on the native species was conducted in the upper Kabompo River. We hypothesized that exotic and native species would show no dietary niche overlap than among natives. A total of 7 species were collected, out of which 140 specimens had their stomach contents analyzed. Fishes were grouped into 3 major feeding groups; microphages, macrophages and carnivores, and omnivores. They were also grouped into size classes of <50, 51-100, 101-150 and 151-302 mm TL. Exotic O. niloticus had a larger dietary niche than native species (78% and 22% respectively). The dietary niche overlap between exotic and native species at size classes <50 and 51-100 mm TL was significantly high (F=0.084, p < 0.05). Dietary niche overlap among the natives at size class <50 mm TL was low (F=2.13, p > 0.05). Dietary niche overlap for Oreochromis macrochir, Pseudocrenilabrus philander and Tilapia sparrmanii at size classes 51-100 mm and 101-150 mm TL was high (F=0.27, p < 0.05). There was no clear evidence of ontogenetic diet shift among the natives, except for S. macrocephalus that showed ontogenetic diet shifts at 51-100 mm TL size class. The results on dietary overlap indicate intraspecific completion between exotic O. niloticus and natives, which may have a major impact on food web structure in the upper Kabompo River and may explain the decrease in population of some natives.