The Biology of the Ten Pounder, Elops Lacerta (Val) In the Freshwater, Estuarine and Marine Environments

Author: Ugwuba, Obih Alex

Supervisor: Kola Kusemiju

Aspects of the biology of the ten-pounder Elops Lacerta (Val) in the freshwater, brackish and marine habitats were investigated. The investigations covered the taxonomy, racial study, distribution, age and growth, food and feeding habits and reproduction. Work was also carried out on the physicochemical features of the different environments. Meristic and morphometric characters were employed in the taxonomy and racial studies. Juvenile E. Lacerta was widely distributed in the Lekki and Lagos Lagoons while adults existed off the Lagos Coast. The greatest abundance of adult ten-ponders was within depths of 10 - 20m especially in the shallow waters after the harbour entrance. The specimens examined ranged from 5.8 - 24.4cm in Lekki Lagoon, 6.2 - 23.3cm in Lagos lagoon and 16.6 - 34.1cm off the Lagos Coast. Ageing of the species was carried out using the otolith, scale, opercula bone and Pettersen's length-frequency methods. Results from the later show three age groups 0 - 1, 1 - 2 and 2 - 3 years old in the species. The fish spends at least one year in the Lagoons and fish in the 1- 2 and 2 - 3 years old groups existed mainly off the Lagos Coast. The pattern of growth in the three habitats was nearly isometric. The food items consisted of fish, crustacea, insects, and gastropods. E. Lacerta in Lekki Lagoon fed more on fish, in Lagos Lagoon it fed on fish as well as crustacea while those off the Lagos Coast fed more on crustacea mainly shrimps. Insects were detected in stomachs only in Lekki Lagoon while gastropods occurred in stomachs from Lagos Lagoon and off the Lagos Coast. The occurrence of ripe, ripe running and spent fish in all the months indicated that spawning occurred in the species throughout the year. Fecundity estimates ranged from 49,802 - 151,481 while egg diameter ranged from 0.48 - 0.81mm. The gonad maturation stages were classified as immature, immature and developing, ripening (1 and 2) ripe, ripe running and spent stages. A racial study of E. Lacerta showed that though there were slight morphological variations between the populations from the three environments, differences were found to be statistically insignificant indicating that the populations from the three environments were not genetically separable.