Some aspects of the biology of the stargazer mountain catfish, Amphilius uranoscopus (pfeffer); (Siluriformes: Amphiliidae) indigenous to Kenya streams

摘要

A study on some biological parameters of the mountain catfish, Amphilius uranoscopus Pfeffer 1889 (Silurifomes: Amphiliidae), was carried out in the Thego stream on the slopes of Mount Kenya from February to December 2002. Physical and chemical profiles of the Thego show that the water quality parameters is typical of high altitude streams with temperatures rarely exceeding 18pC, DO ranging from 7.9 to 8.2 mg lp# and relatively high conductivity (97-137 oS cmp#) typical of perturbed lotic environments. A total of 1010 fish were caught by an electro-fisher, with sizes ranging between 8 and 24 cm fork length. The population structure had a unimodal distribution with maxima at 14-16 cm. The length-weight relationship showed relatively narrow range in the slope ranging from 2.61 in April to 2.98 in February 2002, thereby suggesting isometric growth pattern. The fitted growth pattern of A. uranoscopus showed an asymptotic length (L[infinity]) of 28.5 cm and a growth curvature (K) of 0.56 yearp# resulting in an estimated natural mortality coefficient (M) of 0.90 yearp#. The Fulton's condition factor (K) was also relatively stable with a peak in April (0.92 pl 0.21) and lowest value in June (0.86 pl 0.10). As A. uranoscopus is not under commercial exploitation, the seemingly depressed population is possibly attributed to the introduced exotic rainbow trout that heavily predates on the species and environmental perturbations arising from changes in land use. The implications of such changes on A. uranoscopus are discussed.