Observations on the age and growth of <i>Brycinus nurse</i> (Paugy 1986) - Pisces: Characidae in Asa Reservoir, Ilorin, Nigeria

Abstract

A total of 1,190 specimens of Brycinus nurse (Paugy 1986) caught in Asa Reservoir from November 1991 to October 1993, were analyzed to determine the age and growth using scales and the integrated methods. Obtainable data from the observed, back calculated and Paulys integrated method indicated that the species attained 13.76cm, 15.49cm, 17.02cm, 17.87cm, 21.00cm and 23.00cm in the first, second, third, fourth, fifth, sixth and seventh year of life respectively. Values obtained from back calculated lengths were lower as compared to those of the observed lengths while those of integrated values were higher than the observed, although the difference was not significant (P>0.05). Average values of ultimate or asymptotic length (L) and the growth coefficient (K) of 27.67 and 0.66 respectively were obtained. The smallest specimen of B. nurse obtained measured 7.56CM (T.L) and weighed 22g while the largest specimen measured 22.60cm (T.L) and weighed 98.91g. The b value obtained was 3.012 indicating that the species exhibited isometric growth. B. nurse attained rapid growth within the first two years with growth decreasing thereafter. Female specimens were observed to grow faster than the males in the first two years of growth. Similarly the females dominated the early age groups (1+ and 2+) with males dominating the age group 3+. A prosperous commercial fishery exists for B. nurse in Asa reservoir, which could be exploited sustainably by the use of the appropriate gill nets.

Key Words: Brycinus nurse, scales, age determination, growth

Tropical Freshwater Biology 11 (2002) 23-35