Comparison of Otolith Readability and Reproducibility of Counts of Translucent Zones Using Different Otolith Preparation Methods for Four Endemic Labeobarbus Species in Lake Tana, Ethiopia

Gebremedhin Gebremedhin,Bruneel Bruneel,Anteneh Anteneh,Bekaert Bekaert,Getahun Getahun,Goethals Goethals,Torreele Torreele

doi:10.3390/w11071336

Gebremedhin Gebremedhin, Bruneel Bruneel + Show 5 more

Open Access

https://doi.org/10.3390/w11071336

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Journal: Water	Publication Date: Jun 28, 2019
Citations: 5	License type: CC BY 4.0

Affiliation: Ghent University, Bahir Dar University, Addis Ababa University

Abstract

The analysis of fish age data is vital for the successful conservation of fish. Attempts to develop optimal management strategies for effective conservation of the endemic Labeobarbus species are strongly affected by the lack of accurate age estimates. Although methodological studies are key to acquiring a good insight into the age of fishes, up to now, there have not been any studies comparing different methods for these species. Thus, this study aimed at determining the best method for the endemic Labeobarbus species. Samples were collected from May 2016 to April 2017. Asteriscus otoliths from 150 specimens each of L. intermedius, L. tsanensis, L. platydorsus, and L. megastoma were examined. Six methods were evaluated; however, only three methods resulted in readable images. The procedure in which whole otoliths were first submerged in water, and subsequently placed in glycerol to take the image (MO1), was generally best. Except for L. megastoma, this method produced the clearest image as both the coefficient of variation and average percentage error between readers were lowest. Furthermore, except for L. megastoma, MO1 had high otolith readability and no systematic bias. Therefore, we suggest that MO1 should be used as the standard otolith preparation technique for the first three species, while for L. megastoma, other preparation techniques should be evaluated. This study provides a reference for researchers from Africa, particularly Ethiopia, to develop a suitable otolith preparation method for the different tropical fish species.

Highlights

The endemic Labeobarbus species in Lake Tana are the only remaining known intact species flock of large cyprinids in the world [1]
Fish size ranged from 10–65 cm fork length (FL) for L. intermedius, 12–45 cm FL for L. tsanensis, FishL.size ranged from length (FL) forThe
L. tsanensis, and L. platydorsus were within the length groups of 15–20 cm (18 cm mid-length) and intermedius, L. tsanensis, and L. platydorsus were within the length groups of 15–20 cm (18 cm mid20–25 cm (23 cm mid-length), while specimens with a fork length of more than 33 cm of were rarely length) and 20–25 cm (23 cm mid-length), while specimens with a fork length of more than 33 cm of caught

Summary

Introduction

The endemic Labeobarbus species in Lake Tana are the only remaining known intact species flock of large cyprinids in the world [1]. Labeobarbus species are the most economically and ecologically important fishes in Lake Tana Because of their migratory and spawning aggregation behaviours [2] and specialized endemic characteristics [3], Labeobarbus populations are highly susceptible to illegal fishing and environmental degradation. As a result, their abundance has markedly declined [4,5,6,7] and six of the seventeen species have already been listed in the IUCN (International Union for Conservation of Nature) Red List as threatened species [8,9].

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