Some Aspects Of The Biology Of Papyrocranus Afer And Xenomystus Nigri (Family Notopteridae) In The River Osse, Southern Nigeria

Abstract

Specimens of two notopterids, Papyrocranus Afer and Xenomystus Nigri were collected from Osse River at Ikoro between December 2002 and August 2003 and examined for morphometric features, condition factor and food and feeding habits. The standard length of P. Afer ranged from 13.7-38.1 cm and X. Nigri, 8.3-16 cm. The mean condition factor of P. Afer was 0.96 and X. Nigri was 1.18. Generally, specimens of higher standard length had lower condition factor than those of lower standard length. A significant negative regression (P<0.001) of condition factor on the standard length of specimens of these species was also recorded. In P. Afer the average proportion of anal fin base length to the standard length was 74.90%, while in X. Nigri the mean proportion of the anal fin base length to the standard length was 79.86%. The proportion of the serrated belly to the standard length was however greater in P. Afer (13.31%) than X. Nigri (10.39%). The occurrence method showed that in P. Afer, aquatic insects constituted 92.86%, shrimps (57.14%), worms (50%) and fish (35.71%), while in X. Nigri, the percentage occurrence of aquatic insects was 75%, worms (62.5%), molluscs (43.75%), detritus (37.5%) and shrimps (1.25%). The numerical method showed that in P. afer the aquatic insects dominated with 34.21 %, followed by fish (26.32 %), shrimps (21.05 %) and worms (18.42 %), whereas in X. Nigri, the worms dominated with 56.82 %, followed by molluscs (26.52 %) and aquatic insects (15.15 %). The adaptive significance of ventral serration and the extensive anal fin base in the feeding ecology of these species is discussed.

Keywords: Belly midventral serration, extensive anal fin base, feeding ecology, morphometric features.

Tropical Freshwater Biology Vol. 16 (2) 2007: pp. 9-19