Structure and composition of otoliths of Cape hake Merluccius capensis

Abstract

A study of the structure and the chemical composition of Cape hake otoliths has shown that they are composed of aragonite and a little fibrous protein. The aragonite is arranged in prismatic structures radiating from the centre to the margin of the otolith. Each prism contains aggregates of crystalline fibres, which are in turn made up of numerous microcrystals. The constituents of the otoliths are laid down in a regular manner associated with growth, typical of all teleosts, each increment being composed of a continuous and discontinuous unit. The discontinuous unit is relatively less calcified. The width of the increment depends upon when it was formed. The chemical composition of the protein (otolin) seems to change with age. The acidic and the hydrophobic amino acids increase, the basic amino acids decrease and the polar amino acids and glycine remain stable. This increase in the rate of deposition of the acidic amino acids is probably related to the enhanced mineralization in the otoliths of older fish. © 1986 Taylor & Francis Group, LLC.