Full Length Research Paper

Length- weight relationships and condition factors of Oreochromis niloticus and Chrysichthys nigrodigitatus in Mahin lagoon, Nigeria

Josef Bamidele Bolarinwa

Abstract

A study of the icthyofauna resources of Mahin lagoon of Ondo State of Nigeria conducted for 18 months (June 2011-December, 2012) revealed the presence of 67 finfish species with the clariids( Clarias gariepinus and Heterobranchus bidorsalis) and cichlids (Oreochromis niloticus and Coptodon zilli) dominating the stock accounting for 42% and 16% respectively. Other predominant families were ’Claroitedae’(Chrysichthys nigrodigitatus) with 9.2% contribution, ’Channidae’(Parachanna africana) with 8.7%, Osteoglossidae (Heterotis niloticus) with 7.1%, Gymnarchidae( Gymnarchus niloticus), Mugilidae (Mugil cephalus) and Clupeidae (Ethmalosa fimbriata). The length-weight relationships and condition factor ‘K’ of 480 specimens of O. niloticus and C. nigrodigitatus of Mahin Lagoon were investigated for 6 months (May-October, 2013). Results showed that the growth patterns of C. nigrodigitatus and O. niloticus) were described by the formula. Log W = -0.253 + 2.102 log TL and log W = +0.590 +1.53 log TL respectively. A comparatively low positive correlation coefficient ’r’ of 0.60exists between the length and weight of O. Niloticus while that of C. nigrodigitatus was 0.88. The b values of O. niloticus and C. nigrodigitatus at 1.53 and 2.10 respectively showed the growth patternsof both fishes were negatively allometric. K factor of 5.22 was recorded for O. niloticus while that of C. nigrodigitatus was 3.84. The fact that ‘K’ value of O. niloticus was higher than that of C. nigrodigitatus shows higher suitability of Mahin lagoon for the former. However, there is still a need to conduct a more indepth research on the physiochemical parameters of the lagoon in view of its on-going industrialisation and crude oil exploration around the lagoon.

Key words: Allometry, condition factors, length-weight relationships, species composition.

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