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Alternate Title

Validation of Annual Growth-Zone Formation in Gray Triggerfish Balistes capriscus Dorsal Spines, Fin Rays, and Vertebrae

Abstract

The goal of this study was to validate annual growth-zone formation in the gray triggerfish Balistes capriscus dorsal spines, fin rays, and vertebrae. Adult gray triggerfish (n = 4) were chemically marked by injecting with 50 mg of oxytetracycline (OTC) per kilogram body mass and reared in a 2,300-liter aquaculture tank. Fish were exposed to ambient light and water temperature mimicked bottom temperatures observed at an approximately 30-m depth in the northern Gulf of Mexico. Fish died after 262 d and their first dorsal spines, pectoral fin rays, and vertebrae were extracted and sectioned. One translucent zone formed distal to the OTC mark in all hardpart types during the study period. Additional fin rays and vertebrae with corresponding dorsal spines were sampled from fish (n = 27 and 59, respectively) during fishery-independent surveys to compare translucent zone counts between hardparts. There was a significant difference between translucent zone counts between fin ray and dorsal spine sections (tdf = 1,25 = 23.15, P = 0.004). Fin ray counts on average were one zone greater than dorsal spine counts. Translucent zone counts in vertebrae were similar to those counted in dorsal spines with no significant difference between structures (tdf = 1,57 = 1.90, P = 0.062). The percentage of dorsal spines with translucent margins increased in winter months, peaking in February, and dropped to the lowest values in summer. The combined results of this study validate annual translucent zone formation in gray triggerfish hardparts, with dorsal spines being the preferred ageing structure for production ageing.

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