"The Biology of the Clupied, Ilisha Africana (Bloch) Off the Nigerian Coast"
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Date
1982-01
Authors
Marcus, O.
Journal Title
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Publisher
University of Lagos
Abstract
Aspects of the biology of Ilisha Africana (Bloch) caught off the Nigerian Coast were studied. These included the taxonomy, distribution, age and growth, food and feeding habits, reproduction and racial studies. The use of meristic and morphometric characters was employed in the taxonomy study. I. africana was widely distributed along the Nigerian Coast within depths of 10 - 50m. The the greatest abundance occurred at depths between 40m and 50m. The size range of the specimens examined was between 4.2, and 28.7cm. Ageing of the species was carried out using the burnt otolith technique and the maximum age attainable was found to be 5 years while the size and age at maturity were 12.0cm and 1 year respectively. Growth was found to be isometric in this species. The food and feeding habits were studied using the numerical, volumetric and frequency of occurrence methods. The major food items of I. africana consisted of crustaceans, fish, Larvae and molluscs. The larger fish fed more on larger food items while the diets of the smaller fishes consisted mostly of the smaller food items. Diets of fishes from shallow depths consisted of a greater variety of good organisms than the diet of fishes from the deeper waters. The occurrence of ripe, ripe running and spent fish in all months of the year indicated that spawning occurred in the species throughout the year. However, higher percentages in the months of June to December and the higher values of the gonadosomatic indices (GSI) from May to December was used in delimiting the peak spawning season. Period of peak spawning coincided with the period of higher condition factors in the species. Fecundity estimates ranged from 2,029 to 11,687 while the egg diameter ranged from 0.57 to 1.35 mm. The gonad maturation stages were classified as immature, ripening 1, ripening 2, ripe, ripe running and spent stages. The histological growth of the ovarian egg was monitored and the stages involved in oogenesis of I. africana were classified as oogonium, primary oocyte, primary vitellogenesis, secondary vitellogenesis, tertiary vitellogenesis, hyaline oocyte, and corpora atretic. A racial study of I. Africana collected from Lagos Coast, off Benin, Brass and Bonny Rivers showed that they were not genetically separable populations. Significant differences were found only in the final counts of specimens off Lagos Coast as compared with the other locations.
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Keywords
Ilisha Africana , Fishes--Reproduction
Citation
Marcus, O. (1982), "The Biology of the Clupied, Ilisha Africana (Bloch) Off the Nigerian Coast". University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation Abstracts. 209pp.