Fecundity and egg size variation in Tilapia zillii (gervais) and Tilapia mariae (boulenger) from Lekki lagoon, Nigeria.

Abstract

Tilapia zillii and Tilapia mariae collected from the landings of fishermen operating on Lekki Lagoon between February and November, 2000 were examined for fecundity and egg size. Fecundity was determined using the wet weight method while egg size was measured under a binocular microscope with the aid of a standardized calibrated eye piece. Graphical comparisons of Gonadosomatic Index (GSI), Absolute Fecundity (AF), and Relative Fecundity (RF), were made by standardizing fish to common weight. ANOVA result showed that T. zillii had significantly higher GSI (P = 0.01), AF (P < 0.01) and RF (P < 0.01), than T. mariae, which indicates that T. zillii allocates a higher percentage of its energy to egg production. This greater reproductive success was advanced as a possible reason for its higher population than T. mariae in the lagoon. A maximum mean egg size of 2.29 mm observed in both species was larger than those reported for the great lakes of East Africa. The T. zillii and T. mariae populations in the Lekki Lagoon may thus be considered to fall nearer the k-extreme of the r/k MackArthur and Wilson life history style continua than those of the great lakes of East Africa.

Keywords: Fecundity, Egg Size, Gonadosomatic Index, Parental Care, Tilapia zillii, Tilapia mariae