Scanning electron microscope observations of the organic matrix in the otolith of the teleost fish Fundulus heteroclitus (Linnaeus) and Tilapia nilotica (Linnaeus)

Abstract

Scanning electron microscope observations of sagitta otoliths of Fundulus heteroclitus (Linnaeus) and Tilapia nilotica (Linnaeus) have revealed that the “discontinuous zone” is a narrow band of organic matrix consisting of fibers ≈900 Å thick, that in turn are composed of thin fibers ≈200 Å thick. The “incremental zone” is the crystalline layer with crystals elongated perpendicular to the otolith periphery that are usually terminated at the discontinuous zones. The crystals are embedded in organic matrix fibers that appear similar to and continuous with the fibers of the discontinuous zones. Frequently, these fibers aggregate into matrix sheets. Based on these findings, a possible process of otolith formation is proposed.