EXPERIMENTAL ASSESSMENT OF THE EFFECT OF TEMPERATURE AND SALINITY ON ELEMENTAL COMPOSITION OF OTOLITHS USING LASER-ABLATION ICPMS

Laser ablation - inductively coupled plasma mass spectrometry (LA-ICPM S) is a new technique that can be used for the multielemental analysis of otoliths at specific loci. This method was used to sample the otol iths of Atlantic croaker (Micropogonias undulatus), reared under diffe rent constant regimes of temperature and salinity, to determine whethe r the elemental composition of otoliths changes ontogenetically. Each otolith was sampled at a number of loci, beginning at the center and t hen every 500 mu m along the longest axis to near the edge; of 23 isot opes measured simultaneously at each locus, 18 were standardized to Ca -48 and included in analyses. The elemental composition at otolith cen ters and near their edges differed significantly amongst treatments, w ith the effect of temperature a stronger influence. Elemental composit ion also varied across otoliths from within treatments, indicating end ogenous effects. Ontogenetic patterns differed amongst treatments, ind icating that endogenous control was mediated by the external environme nt. Otoliths of fish from one tank where the physical conditions were switched, showed greater variation in the multielemental signal than t hat resulting only from ontogenetic change. All analyses indicated tha t otolith formation is the product of numerous interactive exogenous a nd endogenous processes, including water temperature, salinity, and on togeny.