Does eel metamorphosis cause a breakdown in the tenets of otolith applications? A case study using the speckled worm eel (Myrophis punctatus, Ophichthidae) Perce M. Powles, Jonathan A. Hare, Elisabeth H. Laban, and Stanley M. Warlen Abstract: Several basic tenets of otolith research have been questioned recently with regard to eel metamorphosis. Specifically, some researchers have suggested that otolith increment formation is not daily, and otolith material may be resorped during metamorphosis. We conducted a rearing experiment to test the hypothesis that increment formation is daily and that the otolith continues to grow during eel metamorphosis. We marked the otoliths of wild-caught Myrophis punctatus leptocephali and reared these fish through metamorphosis. Metamorphosis was characterized by a decreasing standard length, pre-anal length, and body depth accompanied by an increase in pigmentation and a change in behavior. Increment formation was daily or near-daily through metamorphosis, and the otolith continued to grow during meta- morphosis. Thus, the basic tenets of otolith application apply to eel metamorphosis, and non-daily ring deposition and resorption should not be used as explanations for otolith characteristics of eels (e.g., back-calculated hatch dates) unless demonstrated experimentally. Résumé : Des études récentes sur la métamorphose des anguilles ont été l’occasion de mettre en doute certaines pré- misses des analyses basées sur les otolithes. Concrètement, des chercheurs ont allégué que la formation des couches de croissance n’est pas un phénomène journalier et qu’une partie du matériel des otolithes peut être résorbé durant la mé- tamorphose. Nous avons mis au point une expérience d’élevage afin de vérifier l’hypothèse selon laquelle la formation des couches est un phénomène journalier et que les otolithes continuent à croître durant la métamorphose des anguilles. Nous avons marqué les otolithes de leptocéphales de Myrophis punctatus capturés en nature et nous avons élevé les poissons jusqu’à la métamorphose. La métamorphose se caractérise par une réduction de la longueur standard, de la longueur pré-anale et de la profondeur du corps, ainsi que par une augmentation de la pigmentation et un changement de comportement. Durant la métamorphose, l’addition de couches de croissance se fait sur une base journalière ou quasi-journalière et les otolithes continuent de croître. Ainsi, les prémisses de base de l’utilisation des otolithes s’appliquent à la métamorphose des anguilles; on ne doit donc pas invoquer la déposition non journalière des anneaux ni la résorption pour expliquer les caractéristiques des otolithes des anguilles (par ex., dans le rétro-calcul des dates d’éclosion) à moins de posséder des preuves expérimentales. [Traduit par la Rédaction] Powles et al. 1468 Introduction The analysis of otolith microstructure and chemistry has led to many major advances in fish ecology. Otolith-derived ages have provided time scales for the duration of the larval stage (Victor 1986; Wellington and Victor 1989). Otolith size as a proxy for fish size has been used to examine size- selective mortality (Meekan and Fortier 1996; Hare and Cowen 1997; Vigliola and Meekan 2002). Growth and mortality rates based on otolith ages have contributed to understand- ing the processes that affect larval and juvenile fish survival (Crecco and Savoy 1987; Rutherford and Houde 1995). Pat- terns in spawning and settlement based on otolith-derived ages have been used to evaluate links between reproduction and recruitment (Robertson et al. 1999). Otolith chemistry has yielded new insights into the stock structure of species (Thorrold et al. 2001) and the environmental histories of in- dividuals (Secor et al. 2001; Tsukamoto and Arai 2001). Can. J. Fish. Aquat. Sci. 63: 1460–1468 (2006) doi:10.1139/F06-052 © 2006 NRC Canada 1460 Received 9 March 2005. Accepted 20 February 2006. Published on the NRC Research Press Web site at http://cjfas.nrc.ca on 2 June 2006. J18595 P.M. Powles. Biology Department, Trent University, Peterborough, ON K9J 7B8, Canada. J.A. Hare, 1,2 E.H. Laban, and S.M. Warlen. National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), National Centers for Coastal Ocean Science (NCCOS), Center for Coastal Fisheries and Habitat Research, 101 Pivers Island Road, Beaufort, NC 28516, USA. 1 Corresponding author (e-mail: jon.hare@noaa.gov). 2 Present address: NOAA, National Marine Fisheries Service (NMFS), Northeast Fisheries Science Center (NEFSC), Narragansett Laboratory, 28 Tarzwell Drive, Narragansett, RI 02882, USA.