Aberrant otoliths in juvenile flounder Platichthys flesus (L.)
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1
FCUP - Faculty of Sciences Porto University, Portugal
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2
Institute of Earth Sciences, FCUP pole and DGAOT, FCUP, Portugal
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3
CIIMAR - Interdisciplinary Centre of Marine and Environmental Research, Portugal
Anomalous otolith formation has been reported in freshwater and marine fish species. The prevailing anomaly is the deposition of vaterite instead of aragonite, resulting in different otolith shape and transparency. In this study we report high occurrence rates of anomalous otoliths in juvenile flounder collected in the river Minho estuary (NW Portugal). Several pairs of otoliths were randomly selected from juvenile fish collected between 2013 and 2015, in two estuarine areas, and visually inspected on both sides for the presence of anomalies. Most anomalies consisted of depressions, projections or holes in different parts of the otolith. Distribution of irregularities was examined in relation to site of collection and fish total length. At the site with higher salinity, most otolith pairs were normal. In contrast, at the tidal freshwater station, 43% of the pairs examined were abnormal. In general, both otoliths were affected but the left one presented more extreme changes. The occurrence of anomalies seems to be related to fish size since these were only found in fish smaller than 7.5 cm. Preliminary morphometric analyses indicate that abnormal otoliths have the same proportions as normal ones, but the former seem heavier, for the same sized fish. It is presently unclear how these anomalies affect fish growth or survival. Raman microspectroscopy was used to determine the mineral phases (i.e. type of CaCO3 polymorph) in one normal and one abnormal otolith, revealing crystals of aragonitic-type in both cases. SEM-EDS analysis corroborated Raman results and did not reveal differences in chemical composition between abnormal and normal zones but further studies are needed.
Acknowledgements
This work was done in the framework of PEEC 2015 (Programa de Estágios Extra-curricular) from FCUP (Porto University). Vânia Freitas and Joana Campos were supported by post-doc grants (SFRH/BPD/75858/2011 and SFRH/BPD/71205/2010 respectively)from Fundação para a Ciência e a Tecnologia (FCT, Portugal) co-financed by national funds (MCTES) and by the European Social Fund (POPH-QREN-FSE).
Keywords:
Raman microspectroscopy,
Flounder,
otolith anomalies,
Minho estuary,
Tidal Freshwater Wetlands
Conference:
XV European Congress of Ichthyology, Porto, Portugal, 7 Sep - 11 Sep, 2015.
Presentation Type:
Poster Presentation
Topic:
Otoliths as a tool to study fish life cycles
Citation:
Neves
V,
Guedes
A,
Campos
J and
Freitas
V
(2015). Aberrant otoliths in juvenile flounder Platichthys flesus (L.)
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Front. Mar. Sci.
Conference Abstract:
XV European Congress of Ichthyology.
doi: 10.3389/conf.fmars.2015.03.00106
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Received:
19 Nov 2015;
Published Online:
21 Nov 2015.
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Correspondence:
Dr. Vânia Freitas, CIIMAR - Interdisciplinary Centre of Marine and Environmental Research, Porto, Portugal, vpfreitas@ciimar.up.pt