Can we model otolith growth and opacity patterns as a response to environmental factors and fish metabolism ? A DEB-based framework

This report presents a conceptual and numerical model of the formation of fish otoliths within a DEB-based (Dynamic Enerby Budget) framework. The proposed model relies on two mains assumptions: 1. The precipitation of the calcium carbonate in the endolymph is controlled by organic precursors; 2. The activity of these organic precursors can be modelled as a DEB product, i.e. as a function of metabolic fluxes, such as somatic growth and maintenance fluxes; 3. The existence of a temperature-driven effect on the dynamics of the precipitation of calcium carbonate for given conditions in the activities of ionic precursors; From these assumptions, a DEB-based otolith model is described relating the dynamics of the otolith growth and opacity to temperature and feeding conditions. An extension to the simulation of otolith images is presented. This model is shown to conform to a number of well-known facts on otolith. Besides, comparisons between model simulations and real otolith patterns are reported for different cases: otolith data from rearing experiments and otolith patterns from two different cod stocks, namely Barents sea cod and North Sea cod. This example illustrates the great potential of the proposed approach