Strontium Labelling for Verifying Daily Growth Increments in the Statolith of the Short-Finned Squid (Illex illecebrosus)

Shrimp soaked in strontium chloride solution were fed to short-finned squid (Illex illecebrosus). The strontium was deposited in the statolith of the squid where, with the use of an electron microprobe, it was detectable as a distinct band on the ground surface of the statolith. Strontium X-ray maps and corresponding back-scattered electron images in the atomic contrast mode were obtained. Use was made of a strontium X-ray line profile to discriminate between markings deposited only 2 d apart. Micrographs were compared with light micrographs to verify the daily growth increments.