Hidden morphological and structural characteristics in scales of mullid species (Teleostei: Mullidae) using light and scanning electron digital imaging

Abstract

The scale morphology of nine Mullidae taxa consisting of three genera and nine species from the Persian Gulf and the Gulf of Oman was described and compared using light and scanning electron microscopy from four different body regions. The general scale type in the studied mullid species was ctenoid except in the head region of Mulloidichthys vanicolensis and Parupeneus margaritatus, which had cycloid scales. The scales demonstrated a large focus with the central or centro‐posterior position. The large variations of scale morphology were observed for the scales from different body regions of a single species. The shape of focus was in five types with the round type being the most common. In the scales of most examined species, there were 5–6 radii present in the anterior field. No radii exist in the lateral and posterior fields, and the radii orientation was parallel in all the studied species. The rostral margin of scales represented five types among the studied species; waved (M. vanicolensis), smooth in (P. rubescens), dentate (Upeneus doriae), scalloped (U. vittatus), and fluted (U. tragula). The lepidont shape varied among the species from blunt to flat, pointed, tiny, sharp, pointed, triangle, short, and long. The results also showed that the relative scale size has a desirable contribution to separate the examined genera. The scale morphological‐based tree was largely consistent with the known systematics of the studied fishes. It was concluded that variation of scale characters has probably taxonomic and even phylogenetic information in both species and genus levels in the studied mullid fishes. However, variation of scale morphology between body regions, as shown in this study, suggests that scale characters should be used cautiously for taxonomic studies of these fishes.

Morphological and microstructural characteristics of scales in longnose goby Awaous jayakari (Teleostei: Gobiidae): Light and scanning electron microscopy approaches

“…The position of the focus can be classified according to the focal index, as follows: <0.20, anterior; 0.21–0.40, antero‐central; 0.41–0.60, central; 0.61–0.80, postero‐central; >0.81, posterior (Echreshavi, Esmaeili, Teimori, Safaie, & Owfi, 2021). In A. jayakari , the focus index varied from 0.70 to 0.95 with a mean of 0.86 (±0.07) in all studied fishes and was not significantly different between three size classes, hence, based on the mean value, key scales show posteriorly located focus.…”

Scales surface topography: Comparative ultrastructural and decorative characteristics of a modern elasmoid fish scales in a cyprinid fish, Garra shamal (Teleostei: Cyprinidae) using digital optical light and scanning electron microscope imaging

“…Pink: Southwestern Arabian Coast, green: Oman Mountains, and yellow: Arabian Interior imaged using a Nikon Eclipse 80i digital imaging head connected to a computer. Digital images were then used for morphological descriptions and measurements (Echreshavi et al, 2021), and for scanning electron microscopy, they were immediately mounted on aluminum mounts with double-backed tape to prevent curling of scale margins.…”

“…Scale size was measured, because scale size varies between the different body parts of a single fish specimen (Echreshavi et al, 2021;Sabbah et al, 2020). Five linear parameters of the scale shape/size were measured using the ImageJ ver.1.8.0 software (Schneider et al, 2012) 2c) (Echreshavi et al, 2021).…”

“…Scale size was measured, because scale size varies between the different body parts of a single fish specimen (Echreshavi et al, 2021;Sabbah et al, 2020). Five linear parameters of the scale shape/size were measured using the ImageJ ver.1.8.0 software (Schneider et al, 2012) 2c) (Echreshavi et al, 2021). Based on these parameters, five indices were calculated, including two relative scale sizes (J index), shape index (Si index), the scale extension (SE index), and focus index (Fi).…”

“…The linear measurements used for the morphometric analyses and for the estimation of the focal index (Fi) as (a c/ a a 0 ) 100. "a c" is the distance from the outermost part of the anterior field to the focus, "a a 0 " is the distance from the outermost part of the anterior field to the outermost part of the posterior field, and "b b 0 " is dorsal-ventral height (Bräger et al, 2017;Echreshavi et al, 2021;Roberts & Aspy, 1993;Sabbah et al, 2020) T A B L E 1 The terminology of scale features and characters…”