Population dynamics of Chrysichthys nigrodigitatus (Lacépède, 1803) in Ikere-gorge, Oyo State, Nigeria

S.O Ajagbe,I.O Arabambi,O.O Oyewole,F.I Abdulazeez,B.O Fadimu,O.O Oyekan,R.O Ajagbe,M.T Ojubolamo,O.A Ganiyu,I.E Odiaka,O.S Ariwoola,A.O Olomola,D.O Odulate

doi:10.4314/gjas.v56i1.6

Abstract

The growth and mortality parameters of Chrysichthys nigrodigitatus were estimated to assess the sustainability of its exploitation in Ikere-gorge, Oyo State, Nigeria. A total of 1210 of Chrysichthys nigrodigitatus were sampled from fishermen catches between January, 2017 and December, 2018. C. nigrodigitatus were exploited with gillnet, cast net and traps (Malian trap net and bamboo). Total lengths were measured with fish measuring board. The FAO-ICLARM Stock Assessment Tool (FiSAT II) software was used to analyze length-frequency data of the fish. The estimated growth parameters are: asymptotic length is 60.9 cm, growth coefficient is 0.96, optimum length is 38.51 cm; length at maturity is 33.44 cm while length-at-first-capture is 12.62 cm. The estimated mortality parameters are: total mortality is 3.29 per year, natural mortality is 1.43 per year and fishing mortality is 1.86. It was observed that C. nigrodigitatus of Ikere-gorge were more vulnerable to exploitation at sizes less than their length at maturity. Likewise, the exploitation rate (E = 0.57 yr-1) is greater than sustainable exploitation rate (Emax = 0.46 yr-1). This shows that exploitation of C. nigrodigitatus in Ikere-gorge is not sustainable. Therefore, there is need to reduce fishing pressure on C. nigrodigitatus to ensure its sustainability in Ikere-gorge.

Highlights

Fish population is a group of the same species or subspecies of fish that are spatially and genetically separated from other groups (Pope et al, 2010)
The asymptotic length (L∞) of C. nigrodigitatus of Ikere gorge was greater than 44.5 cm reported by Ofori-Danson et al (2002) for C. nigrodigitatus in Lake Volta, Ghana
The growth and mortality parameters of C. nigrodigitatus of Ikere-gorge, Iseyin, Oyo State, Nigeria were estimated in this study

Summary

Introduction

Fish population is a group of the same species or subspecies of fish that are spatially and genetically separated from other groups (Pope et al, 2010). Fish population dynamics is the study of continuous changing of fish stock with time due to factors such as reproduction (recruitment), mortality, migration (immigration and emigration), growth and yield. The objective of studying fish population dynamics is to ensure rational management and conservation of fishery resources (Udoh et al, 2015). S.O. Ajagbe et al (2021) Ghana Jnl. Agric.

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