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Exposing a fish to a solution of strontium chloride hexahydrate (SrCl - 6H20) at approximately 3,000 ppm for 24 hours creates a fluorescent band in the otolith that is visable when viewed with a scanning electron microscope equipped with a backscatter electron detector. By subjecting the fish to a series of exposures, unique patterns are created in the otolith that can be used to identify broodyear and hatchery of origin. This marking procedure is 100% effective, permanent, and has little or no impact on fish health. The fish, however, must be sacrificed in order to recover a strontium-marked otolith. |