Comparative ultrastructure and ornamentation characteristics of scales in gobiid species (Teleostei: Gobiidae) using the scanning electron microscope

To study scale based phylogenetic affinity, the ultrastructure and ornamentation characteristics of body key scales were studied for 12 gobiid species from the Iranian coast of the Persian Gulf including Qeshm and Hormuz Islands and the Makran coast of the Oman Sea using scanning electron microscopy (SEM) technique. The scales were removed from below the first dorsal fin, cleaned in potassium hydroxide solution 1%, and were prepared for the SEM imaging. The presence of both ctenoid and cycloid scales in the studied gobiids was revealed. The focus of ctenoid scales was positioned posteriorly, while the focus of cycloid scales was positioned in the postero-central part of the scale. In all the studied species, radii were located only on the anterior part of the scale, and the primary radii were dominant. Also, there were no granules in the inter circular space, but bifurcation was observed in some circuli. In most species, the teeth-like structures called lepidonts were present on the crest of circuli, which functionally help to firmly attach the scales to the epithelium. The dendrogram of the between-groups-linkage method sorted the gobiid species into the two main groups of five distinct clusters: (a) Cryptocentroides arabicus and Cryptocentrus cyanotaenia (the Cryptocentrus-lineage); (b) Bathygobius meggitti and Bathygobius cocosensis (the Glossogobius-lineage); (c) Coryogalops adamsoni and Coryogalops tessellatus (the Gobius-lineage); (d) Acentrogobius dayi, Istigobius ornatus, Favonigobius reichei, Aulopareia ocellata, and Silhouettea ghazalae (the Gobiopsis-lineage). It seems that the dendrogram topology obtained based on the macro-and microscopic structures of scales, reveals phylogenetic lineages of gobies that have already been proposed for these taxa. Hence, the results of this study are largely consistent with the previous molecular studies on the gobiid fishes and implied that besides other data, the analysis of scale shape and scale-surface microstructures could be served to study the diversification of gobiid species.