Some biological aspects of Brycenus nurse, Hydrocynus forskali, Micralestes Acutidens (Characidae) and Labeo coubie (Cyprinidae) from a reservoir in Ilorin, Nigeria

Abstract

The biological aspects of Brycenus nurse, Hydrocynus forskali, Micraleates acutiden (Characidae) and Labeo coubie (Cyprinidae) were studied from June, 2007 to December, 2008. The variability in egg size (i.e. diameter) were measured using the micrometer eye-piece. The fecundity was estimated by direct enumeration and related to the fish species population while the sex ratio was calculated as a ratio between the numbers of males to females. The mean egg diameter of B. nurse, H. forskali, and M. acutiden were 1133.33 ± 57.74, 1140 ± 54.77 and 875 ± 50 mm respectively, while that of L. coubie was 785.71 ± 86.22 mm. There was variability in the egg size with fish species. The diameter of the eggs also varied within each species. L. coubie contained the highest number of eggs but they were the smallest in size. B. nurse had fairly large number of eggs which were moderate in size. H. forskali and M. acutiden contained moderate number of eggs. L. coubie and B. nurse employed the strategy of the force of number to ensure survival of the offspring. M acutiden employed the strategy of many females with ripe gonads in the population. The reproductive strategy of L. coubie was inefficient but the strategies of B. nurse, H. forskali and M. acutiden were efficient. A sex ratio of approximately 1:1 (male:female) was obtained for B. nurse, H. forskali and L.coubie while a sex ratio of 1:1.5 (male:female) was obtained for M. acutiden.
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Keywords: Fecundity, egg diameter, population.