Ecologie alimentaire de Ichtyoborus besse congolensis Giltay, 1930 (Teleostei: Distichodontidae) de rivière Biaro et son affluent Yoko

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ABSTRACT: A study was conducted on the food ecology of Ichtyoborus besse congolensis of Biaro River and its Yoko tributary in the Yoko Forest Reserve, Democratic Republic of the Congo. It took place over a period of one year: from September 2008 to August 2009. The size and weight of 98 specimens of Ichtyoborus besse congolensis Giltay, 1930 sampled varies from 3.6 to 31.5 cm, with an average of 21.5 cm for the first parameter and of 14-364.4 g, that is, an average of 77.4 g for the second measurement. The analysis of 68 full stomachs of Ichtyoborus besse congolensis Giltay, 1930 under a dissecting microscope shows the dominance of animal origin preys with more or less 6 taxa against some traces of plant fragments. The composition of the diet according to seasonal periods, showed that during relatively dry seasonal period, males appeared to be fish (OCC = 9.6), Heteroptera (OCC = 3.2), Ephemeroptera (OCC = 3.2) and plant fragment eaters (OCC = 3.2), while the trace of molluscs is observed only in females (OCC = 33.3). Shrimps, fins and scales were found in both sexes, but in different proportions, because the large proportion of shrimps was observed in males (OCC = 83.9) while those of fins and scales were dominant in females. More, the emptiness rate was significant only in males. On the other hand, during the rainy season period, females become more opportunist in fish (OCC = 50), shrimps (OCC = 100), fins (OCC = 25) and scales (OCC = 50) thanmales with respectively 16.6 %, 76.6%, 6.6% and 36.6% of occurrence, and the rate of emptiness is higher in females. The food index (FI) and index of relative importance (IRI) of the main categories of preys; preys with high percentages are respectively fish (44%), shrimps (29%), animals fragments (26%). All the other categories of associated preys represent only 1%. It is the rainy period which offers many favorable opportunities for a good growth of fish species.