CONFIDENCE OF OTOLITH AGING THROUGH THE JUVENILE STAGE FOR ATLANTIC MENHADEN, BREVOORTIA-TRYRANNUS

The periodicity of increment formation and our ability to enumerate in crements in sagittal otoliths of Atlantic menhaden are evaluated from hatching through a nine-month period. We studied otoliths from one gro up of field-collected larvae that was marked by immersion in oxytetrac ycline (OTC) and from a second group that was marked by immersion in a lizarin complexone (ALC). Additionally, otoliths from known-age juveni les resulting from an Atlantic menhaden laboratory spawning and rearin g experiment were examined. We determined that, on the average, larval and juvenile Atlantic menhaden form one growth increment per day. We were able to age juvenile menhaden reliably up to 200 days old within a confidence interval (CI) of about 7 days and up to 250 days old with in a CI of about 16 days. We hypothesized that growth rates may have i mpacted the periodicity of increment formation, as well as our ability to count them accurately. The statistically stronogest results were o btained from the ALC-marked fish, which were reared outdoors and displ ayed growth rates (0.67 to 0.95 mm . day(-1)) similar to higher rates observed for juveniles captured from estuarine nursery areas. The peri odicity of increment counts for the ALC-marked fish was less than one per day when growth rates were observed to be less than 0.3 mm . day(- 1). Increments in otoliths from the known-age and OTC-marked fish, whi ch were reared indoors, had lower contrast than their outdoor-reared c ounterparts. Otoliths were sectioned for enumeration on both a transve rse and oblique-transverse plane. With minor exception, no differences in age estimation could be attributed to the orientation of the secti ons.