Relation between Fish Habitat and the Periodicity of Incremental Lines in the Fossil Otoliths

Abstract

There are few research reports on the relationship between fish habitats and the periodicity of the fishes’ incremental lines of otolith fossils. The present study examines this relationship through histological and analytical studies on otolith fossils from Nobori Formation, Pliocene, Japan. The specimens were observed and analyzed using light microscopy, polarizing microscopy, Miniscopy, Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis, electron probe X-ray microanalyzer (EPMA), Raman spectroscopy, and XRD. The otolith crystals were aragonite according to XRD and Raman analysis. The incremental lines contained C, O, and Ca, with Si as a trace element. In the layer between the incremental lines, Si was not detected. The circadian incremental lines were unclear and irregularly observed in both Lobianchia gemellarii and Diaphus gigas. Their behavioral pattern included a diurnal vertical movement. By comparison, for Cetonurus noboriensis, Ventrifossa sp., Sebastes scythropus, and Congriscus megastomus, the circadian incremental lines were evident. The habitat of the fishes that live exclusively on the continental slope is kept constant, and the circadian incremental lines are formed regularly. However, for fishes that spend the day in the deep sea and ascend to the shallow sea at night, the ecosystem, such as seawater temperature and pressure, fluctuates, and the circadian incremental lines become unclear and irregular. The period of the circadian incremental lines of otolith may vary due to differences in the ecosystems.

Keywords

• otolith
• incremental lines
• circadian rhythm
• fossil
• aragonite