Identification of a species diagnostic character for instar and juvenile mud crabs (Genus Scylla)

A species diagnostic character in instar and juvenile Scylla spp. allows for more focused use of resources in farms, enhanced research in wild populations and improved culture practices into preferred species. Species identification using molecular methods entails extraction of soft tissue that can be fatal to early developmental morphs. This prevents downstream applications that require live samples. In this study, a potential species diagnostic character from the frontal lobe spine shapes of 177 wild-caught Scylla crablets was generated. The species of the samples were identified using the molecular internal transcribed spacer 1 and 16S rDNA markers. Fourier transformation was employed on the images of their spines using the software SHAPE and the results underwent discriminant and principal component analyses. This method was able to assign 92.4% of Scylla serrata, 96.2% of S. olivacea and 90.1% of S. tranquebarica to the right species. The frontal lobe spine shapes of each species group were then traced and used as a means for species identification on 50 cultured and 100 wild-caught Scylla crablets through Resemble.js. This method was then able to assign 85.9% of the instars and 84.7% to the correct species, verified using molecular markers. Results of this study show great potential for the use of the frontal lobe spines as a morphological diagnostic character for instars and juveniles. Increased accuracy can be achieved by expanding the reference shape database and inclusion of more Scylla populations across the region.