High incidence of otolith abnormality in juvenile European flounder Platichthys flesus from a tidal freshwater area

ABSTRACT

Otolith abnormality has been reported for a wide range of freshwater and marine fish species. In this study, the sagittal otolith morphology and mineralogy of juvenile European flounder, Platichthys flesus, were examined to describe the incidence and types of structural deformities in this species. Juvenile flounder were collected over the years 2013–2015 in the tidal freshwater section of an estuarine nursery (Minho estuary, NW Portugal). Otolith abnormality was found in 43% of the individuals and, in most cases, occurred in both otoliths. Despite an abnormal mineralogy confirmed by scanning electron microscopy, the morphometry and the mineral polymorph composition of abnormal otoliths did not differ from normal ones (i.e. aragonite). This contrasts with other studies where vaterite and/or calcite were found to replace aragonite in abnormal otoliths. Further studies are needed to elucidate whether abrupt salinity changes associated with habitat transitions may have played a role in the abnormal otolith biomineralization in this species.

RESPONSIBLE EDITOR:

• Audrey J. Geffen

KEYWORDS:

• Abnormal otolith
• sagittae
• flatfish
• nursery
• Raman microspectroscopy
• SEM/EDS

Acknowledgements

This study was done in the framework of the Extracurricular Internship Program (PEEC) of FCUP (Faculty of Sciences of the University of Porto). The authors would like to thank everyone involved in the field and/or laboratory work.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Vânia Freitas http://orcid.org/0000-0003-2097-1704

Additional information

Funding

Financial support was provided by Fundação para a Ciência e a Tecnologia (FCT) through the grants awarded to Vânia Freitas (grant no. SFRH/BPD/75858/2011) and to Joana Campos (grant no. SFRH/BPD/71205/2010). This work also received funding from FCT through the research project ‘Mytag – Integrating natural and artificial tags to reconstruct fish migrations and ontogenetic niche shifts’ (PTDC/MAR-EST/2098/2014), under the Project 9471 – Reforçar a Investigação, o Desenvolvimento Tecnológico e a Inovação (Projeto 9471-RIDTI) and subsidized by the European Regional Development Fund (FEDER, POCI-01-0145-FEDER-016787).