Imaging scale surface topography of an endemic cyprinid fish, Garra sharq from the Arabian Peninsula: An integrated optical light and scanning electron microscopy approach

Abstract

The optical light microscopy and scanning electron microscopy techniques have proven to play a key and noteworthy role in the advancement of morphological studies in general, and in investigating fish scale morphology in particular. These techniques have illustrated several hidden architectural structures in scales that contribute effectively to fish identification and classification. The scale morphological and topological characters such as type, size, shape, lateral surface, focus position, circuli appearance, radii type, lepidonts, and posterior and anterior margin shapes were obtained using macro‐ and microscopic analysis in six body regions for three size classes of Garra sharq, a cyprinid endemic fish of the Arabian Peninsula. The general scale type in the studied G. sharq species was a basal elasmoid cycloid and a sectioned type. As a protective structure, the scales display several specific characteristics including firm attachment to the fish body, overlapping, and thin structure with a high surface area and high strength. These characteristics improve scale resistance to penetration, increase protection against mechanical injury and microbial infection, enhance scale flexibility, reduce fish weight (reduce friction drag), and increase scale transparency. The scales demonstrate plasticity in focus shape, size, and position in the six fish body parts and fish size groups. The examined scales displayed narrow or wide grooves (radii) in three types including primary, secondary, and tertiary present in all four scale fields (anterior, posterior, and laterals), thus a tetra‐sectioned type that is almost specific to the genus Garra. This characteristic also increases scale flexibility. The rostral margin of scales was characterized by the presence of waved and striate types. The lepidont shape and size varied being blunt, flat, pointed, tiny, sharp, short, and long. Some of these scale characters and their morphologies could be used as an alternative tool for identification, classification, and phylogenetic interpretation among the different freshwater fish species and genera.

Scale morphology variability in cyprinid fishes and its significance in taxonomy using light and scanning electron microscopy: A case study of the genus Garra Hamilton, 1822 (Teleostei: Cyprinidae)

“…In the present study, for example, the overall scale shape was irregular round, true oval, round-triangular, irregular pentagonal, hexagonal, irregular hexagonal, pentagonal, or ovoid depending upon the size class and the area of the scale origin on the fish body. The same result has been found in the case of G. shamal (Al and G. sharq (Echreshavi, Al Jufaili, et al, 2022), and also in the scales of tooth-carp fish, Aphaniops hormuzensis (Teimori et al, 2020).…”

“…For example, the mean SI index varied from 3.36 for the key scales of G. rossica to 5.03 for the G. hormuzensis, also the mean SSI varied from 4.01 for the lateral line scales of G. rossica to 5.76 for G. persica. The mean SSI for the key scales of G. shamal (Al Jufaili et al, 2022) and G. sharq (Echreshavi, Al Jufaili, et al, 2022) was 4.44 and 5.03, respectively.…”

“…For LM, after cleaning, as described above, the scales were then put in 30%, 50%, 70%, and 90% alcohol (each for 20 min) for dehydration, and put on filter paper for 24 h to be dried and kept for several hours between glass slides to prevent scale curling (Lippitsch, 1990). images were then used for morphological measurements and descriptions, following Echreshavi, Al Jufaili, et al (2022); . Distinguishable scale characteristics include overall scale shape, presence or absence of focus, circuli appearance, presence of radii, and appearance of lateral, anterior, and posterior fields.…”

“…Numerous fish species have been described based on morphological characteristics for a long time, while molecular traits are becoming increasingly important nowadays. However, knowledge of the shape, structure, and proportions of the different body parts of fishes, including their hard structures (scales, otoliths, teeth, skeleton), is still important for fish species taxonomic and ecological interpretation (e.g., Echreshavi, Al Jufaili, et al, 2022; Echreshavi, Esmaeili, et al, 2022).…”

“…The current framework to categorize scale types and morphology goes back to the studies of Lippitsch (1989, 1990), but has significantly been expanded since then (e.g., Bräger & Moritz, 2016; Wainwright, 2019). Generally, optical light microscopy (LM) and scanning electron microscopy (SEM) techniques play a significant role in the investigation of fish scale surface morphology (= lepidological studies) and have already been used to typify scale morphology of several freshwater and marine species from Iran and the Persian Gulf (Echreshavi, Al Jufaili, et al, 2022; Echreshavi, Esmaeili, et al, 2022; Esmaeili et al, 2019; Gholami et al, 2013; Sadeghi et al, 2020). In addition, recent studies on the evolutionary relationships between various taxa of teleost fishes have evaluated whether there is congruence between phylogenetic hypotheses inferred from molecular data and those from scale morphological data (Esmaeili et al, 2019; Teimori, Motamedi, et al, 2017; Teimori, Motamedi, et al, 2017).…”