Long, J.M. and R.A. Snow. 2018. Post-hatch development of otoliths and daily ring genesis in age-0 Spotted Gar. Transactions of the American Fisheries Society 147:1146-1152. DOI: 10.1002/tafs.10108
Gar (Lepisosteidae) are increasingly being managed as native components of the ecosystem rather than being reviled as they once were. There is a paucity of information on early life history for many species, which would aid their conservation and management. Daily rings in otoliths are useful for determining many early life-history parameters, such as growth rates and date of hatch, but properly interpreting these structures requires additional information on otolith formation. Gar represent an ancient lineage and their otoliths are unlike those of teleost fishes that have been better studied. We used computed tomography (CT) X-ray scanning and oxytetracycline (OTC) marking of a series of known-age fish from hatch through 10-12 days post-hatch (dph) to understand the formation of otoliths in Spotted Gar Lepisosteus oculatus, a species that is of management concern in several parts of its range in North America. Otoliths, sagittae and lapilli, began as a loose associations of otoconia at hatch, fused and hardened into single crystals by 4 dph, in concert with the transition from attached larvae to free-swimming juvenile. Asterisci otoliths were not observed in any of the individuals examined through 12 dph. Oxytetracycline marks were not observed on individuals treated at hatch and variable marks were detected at 1 dph through 5 dph. By 6 dph, 100% of individuals exhibited OTC marks on sagittae and lapilli. Daily rings could not be discerned until fish were marked 4 dph, after which, daily age estimates increased linearly with fish age. Results of this study verify that otoliths (sagittae and lapilli) of Spotted Gar and their daily rings form several days after hatch, in relation to the transition from sessile, attached larvae to free-swimming juvenile.