Improved interpretation of labelled fish otoliths: a cost-effective tool in sustainable fisheries management
T. Niva A B , P. Keränen A , J. Raitaniemi A and H. M. Berger AA The Finnish Game and Fisheries Research Institute, Tutkijantie 2A, 90550 Oulu, Finland.
B Corresponding author. Email: teuvo.niva@rktl.fi
Marine and Freshwater Research 56(5) 705-711 https://doi.org/10.1071/MF04143
Submitted: 12 July 2004 Accepted: 7 March 2005 Published: 24 July 2005
Abstract
A total of 222 pairs of alizarin red S (ARS)-labelled and 75 pairs of unlabelled sagittal otoliths from six hatchery-reared species, including Arctic charr (Salvelinus alpinus (L.)), lake trout (Salvelinus namaycush (Walbaum)), salmon (Salmo salar L.), brown trout (Salmo trutta L.), whitefish (Coregonus sp.) and pikeperch (Sander lucioperca (L.)), were used in blind tests to determine whether sawing a 0.4-mm thick slice from the otolith would improve the interpretation of labelled otoliths. The fish were labelled in 1995–2002. Fish age at labelling varied from two weeks to three months, immersion time from three to six hours and concentration of ARS 50–100 ppm. Blind tests were arranged so that sawed slices were contrasted with entire otoliths using stereomicroscope under UV epi-illumination. According to blind tests, the accuracy of interpretation of ARS-labelled otoliths was 97.0% from the slices and 92.3% from entire otoliths. The role of different filters in detecting false marks owing to autofluorescence is discussed. Cost-benefits of the method are discussed briefly.
Extra keywords: alizarin red S, fluorochrome marker, sagittal otolith, stereofluorescence microscopy.
Acknowledgments
We thank Kimmo Kahilainen, Kari Nyberg, Randi Saksgård and Sami Vesala for offering their time to blind tests. The present study was founded by The Nordic Council of Ministers.
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