Repeatability, Reproducibility, Separative Power and Subjectivity of Different Fish Morphometric Analysis Methods.

Péter Takács,Ádám Staszny,Zoltán Vitál,Árpád Ferincz,Nicholas S Foulkes

doi:10.1371/journal.pone.0157890

Abstract

We compared the repeatability, reproducibility (intra- and inter-measurer similarity), separative power and subjectivity (measurer effect on results) of four morphometric methods frequently used in ichthyological research, the “traditional” caliper-based (TRA) and truss-network (TRU) distance methods and two geometric methods that compare landmark coordinates on the body (GMB) and scales (GMS). In each case, measurements were performed three times by three measurers on the same specimen of three common cyprinid species (roach Rutilus rutilus (Linnaeus, 1758), bleak Alburnus alburnus (Linnaeus, 1758) and Prussian carp Carassius gibelio (Bloch, 1782)) collected from three closely-situated sites in the Lake Balaton catchment (Hungary) in 2014. TRA measurements were made on conserved specimens using a digital caliper, while TRU, GMB and GMS measurements were undertaken on digital images of the bodies and scales. In most cases, intra-measurer repeatability was similar. While all four methods were able to differentiate the source populations, significant differences were observed in their repeatability, reproducibility and subjectivity. GMB displayed highest overall repeatability and reproducibility and was least burdened by measurer effect. While GMS showed similar repeatability to GMB when fish scales had a characteristic shape, it showed significantly lower reproducability (compared with its repeatability) for each species than the other methods. TRU showed similar repeatability as the GMS. TRA was the least applicable method as measurements were obtained from the fish itself, resulting in poor repeatability and reproducibility. Although all four methods showed some degree of subjectivity, TRA was the only method where population-level detachment was entirely overwritten by measurer effect. Based on these results, we recommend a) avoidance of aggregating different measurer’s datasets when using TRA and GMS methods; and b) use of image-based methods for morphometric surveys. Automation of the morphometric workflow would also reduce any measurer effect and eliminate measurement and data-input errors.

Highlights

Morphological characteristics have been of fundamental importance in biology since the beginnings of the discipline
All raw data for geometric methods using body (GMB) and GMS landmark analysis and the variables measured for TRU and TRA analysis are presented in supplementary S1–S4 Tables
None of the variables measured showed any significant correlation with standard length (SL) data after standarisation; all variables were used for further analysis

Summary

Introduction

Morphological characteristics have been of fundamental importance in biology since the beginnings of the discipline. Morphologic investigations compare and analyse “meristic” and/or continuous “measureable” morphometric variables [3]. In the latter case, the morphometric characteristics selected are translated into numeric values so they can be analysed using appropriate statistical methods [4,5]. Morphologic investigations can be applied at various levels. Morphometric surveys can be applied to the entire body [13, 14] or to individual body parts, e.g. a fish scale, vertebra or otolith [15,16, 17, 18], depending on the goal of the survey. The instruments used to measure distance will vary (e.g. tape measure or calipers) and the variables selected for measurement will vary depending on the size and the shape of the individual surveyed

Objectives

Methods

Results

Conclusion