REPRODUCTIVE BIOLOGY OF EXPLOITED POPULATIONS OF THE EMPEROR ANGELFISH, Pomacanthus imperator BLOCH, 1787 ALONG THE KENYAN COAST

Abstract

Substantial proportion of the Pomacanthus imperator are traded in terms of value and quantity and also harvested as food in the artisanal fishery in Kenya. However information on their reproductive biology is scanty. In this study, we investigated the reproductive biology of the P. imperator by collecting specimen from small-scale fishers in selected landing sites along the Kenyan coast for a period of 11 months from March 2014 to July 2014 and from January 2015 to June 2015. A total of 384 specimens (126 males, 192 females and 66 unsexed) were analyzed. Overall sex ratios were significantly differently from 1:1 according to chi-square test (p<0.05). Sizes at maturity (L50) were estimated to be 25cm and 28cm in TL for females and males respectively. Fecundity was estimated to be in the range of 17,790-266,472 with a Mean ±SE of 79,353±11,747 and, was linearly related to total length and ovary weight. P. imperator showed extended spawning period which peaked gradually between March-April based on estimations of the gonad somatic index and monthly proportion of mature individuals. The length-weight relationships (LWRs) for males was best expressed by Log W = -1.553 + 3.022 log TL and for females: Log W=-1.157 +2.772log TL. However, significant difference in both slope (b) and intercept (a) was not observed between sexes (ANCOVA; p=0.18) and therefore, subsequent analysis for Length-weight were pooled. LWR indicated isometric growth both in males and females P. imperator as the allometric coefficient b values were not significantly different from the expected isometric value of 3 (Student’s t-test; p=0.12). Relative condition factor did not vary significantly between the months sampled. The reproductive parameters found from this study provide crucial baseline information for management of this species which has shown high vulnerability to depletion due to overfishing.