Age Structure and Estimated Age at First Maturity of Pellonula Leonensis in Ogobiri River, Niger Delta, Nigeria

Abstract

Pellonula leonensis is an economically important small pelagic clupeid occurring in rivers, lakes, lagoons and other connected aquatic environments in West and Central Africa. Information on age structure is important for understanding population dynamics, growth and reproductive potential. This study investigated the age structure and estimated age at first maturity of Pellonula leonensis from Ogobiri River at Amassoma, Southern Ijaw Local Government Area, Bayelsa State, Nigeria. Specimens were collected at two-week intervals during May, June and July 2013 using gillnets and an Atalla lift-net. Samples were preserved in 10% formalin and subsequently subjected to length-frequency and length-at-age analysis. A total of 242 specimens represented in the sampling records were considered, comprising 50 specimens in the first May sample, 32 in the first June sample, 40 in the first July sample, 42 in the second May sample, 45 in the second June sample and 33 in the second July sample. The length-at-age data showed five relative age classes, with lengths of 5.5, 7.5, 8.5, 9.5 and 10.5 cm, respectively. Absolute growth was greatest between the first and second relative age classes (2.0 cm) and subsequently declined to 1.0 cm per age interval. Relative growth declined from 0.36 in the first age interval to 0.08 in the fifth. Published reproductive evidence for P. leonensis in the Lower Nun River indicates that approximately 50% maturity occurs within 5.5–6.5 cm total length. When this maturity-size range is related to the present length-at-age data, first maturity is estimated to occur between relative age classes 1 and 2, approximately corresponding to 1.0–

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