Geometric morphometric analysis of fish scales for identifying genera, species, and local populations within the Mugilidae

Abstract

Geometric morphometric methods (GMMs) were used to determine if scale morphology can discriminate between genera, species, geographic variants, and stocks of mullet (Mugilidae). GMMs were used because they allow standard multivariate analyses while preserving information about scale shape, which is important in making biological interpretations of results. The method was tested on ctenoid scales from mullets collected from different areas of the Gulf of Mexico and Aegean Sea. Scales were submitted to generalised procrustes analysis, followed by principal components analysis of resulting shape coordinates. Principal component scores were submitted to cross-validated discriminant analysis to determine the efficacy of scale landmarks in discriminating by taxon and population. Fish scale form was least effective in discriminating populations from nearby areas, better when populations are more geographically dispersed, and best between species and genera. Scale form variations reflected previous genetic studies that differentiated congeneric Mugil cephalus and Mugil curema, which are distinct from other Mugilidae. The method is nondestructive, quick, and less costly than genetic analysis, thus allowing many individuals to be screened.