Morphology and Microstructure of Otoliths of Juvenile Fish Species from the Coastal Waters of Ghana

Abstract

This study was conducted on the morphology and microstructure of otoliths of juvenile fish species from Kakum River Estuary, Benya Lagoon and the coastal marine waters near Cape Coast in the Central Region of Ghana, to ascertain their practical use in age and growth studies. Otoliths of twenty–nine (29) species from fourteen (14) families were examined. A linear relationship determined for otolith length – total length, which was described by the equation OL= a + bTL, gave a range of r = 0.22 to 0.96 for commonest species from the three sites, thus suggesting that otolith growth is dependent on somatic growth. Also, otolith morphology was observed to vary among species as the morphological characteristics were species – specific. The otolith microstructure of most of the species showed clear primary growth increments but many lacked a hatch check, hence the embryonic stage of the fish could not be identified in the otolith. Observed patterns of increment deposition for some otoliths appeared to follow a likely weekly pattern whereas others had no clearly-defined patterns of deposition. The mullet species (Mugilidae) however, did not show clear increment deposition as the otoliths had large portions which were obscured hence increment deposition could not be defined for these species. In effect, the results show that the microstructure of otoliths of some species could be used for age and growth studies if increment formation rate can be validated. Also, otolith morphology could provide a base-line information for species identification and differentiation.