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Otolith morphology in the toothcarps of the family Aphaniidae is an important source of taxonomic information. However, little is known about the ontogenetic variation in otolith morphology. In this study, the development of otolith morphology in different life stages of Aphaniops kruppi, an endemic toothcarp of the Arabian Peninsula, is described and discussed. The results reveal (i) a significant correlation between standard length and otolith size (length) in larval and early juvenile stages, (ii) clear differences in otolith morphology between larvae/early juveniles and adults, and (iii) a temporal link between the appearance of the sulcus on the otolith's inner face and lifestyles, that is demersal in larvae and early juveniles, and pelagic in adults. Moreover, our new data on otoliths of Ap. kruppi propose that otoliths of larvae or early juveniles of Ap. kruppi can be recognized by adults not only because of their small size but also based on their short and rounded rostrum and antirostrum and shallow, wide excisura. As the above-mentioned characteristics are also found in the otoliths of juveniles and larvae of several other studied aphaniids, it can be concluded that otoliths are not diagnostic at the species level in Ap. kruppi, and this holds for other closely related species. [ABSTRACT FROM AUTHOR]

Freshwater fishes are facing considerable threats in the Arabian Peninsula which is considered as a highly stressed region in the Middle East. It is predicted that northern Oman is likely to face decreasing rainfall and increasing temperature in coming decades. In this study, we focused on an endemic cyprinid fish Cyprinion muscatense, as a model to investigate impacts of climate change on the mountain fishes inhibiting in this arid region. This species is expected to be strongly affected by climate change because of its limited distribution range in a montane area surrounded by lowlands and sea, limiting the species in shift to other areas. We used an ensemble approach by considering two regressions‐based species distribution modeling (SDM) algorithms: generalized linear models (GLM), and generalized additive models (GAM) to model the species habitat suitability and predict the impacts of climate change on the species habitat suitability. Based on the distribution models, the montane area located in northeastern Oman was identified as the most suitable habitat for this species. Our results indicate that, even under the minimum greenhouse gas emissions scenario (RCP 2.6), climate change will produce a high reduction in its potential future habitats. According to the results of percent contribution, elevation and annual minimum temperature were the most important variables in predicting the species suitable habitats. Results also showed that only a small percentage of suitable habitats for the species within boundaries of protected areas. Therefore, the impact of climate change on the species appears particularly alarming. Although our study was restricted to a single cyprinid freshwater species, decreases in potential habitats are likely predicted for other cyprinid fish species restricted to the mountains of this region, suggesting severe consideration is needed for aquatic systems in future conservation planning, especially for endemic freshwater fishes. [ABSTRACT FROM AUTHOR]

Members of the genus Cyprinion (Cypriniformes: Cyprinidae) are found in the Indus River basin west to the Arabian Peninsula and the Tigris‐Euphrates River drainages (Persian Gulf basin). The taxonomic status of Cyprinion including Cyprinion muscatense is poorly understood when compared to other cyprinid genera. C. muscatense has been considered as a member of the Cyprinion watsoni‐microphthalmum group and a valid species endemic to the Arabian Peninsula. Here, we redescribe C. muscatense based on an integrative morphological and molecular approach and freshly sampled material from several localities in the Oman Mountains ecoregion. The results showed that C. muscatense is distinguished from the other Cyprinion species in the Arabian Peninsula by having a short, thin, and slightly serrated last unbranched dorsal fin ray; the lower number of circumpeduncular scales; lateral line scales; and also scales between the lateral line and the dorsal‐fin origin. Subterminal mouth, presence of one pair of small barbels at the mouth corner, 3–4 unbranched and 9½–10½ dorsal‐fin branched rays, 12–14 pectoral‐fin rays, 7–8 pelvic‐fin rays, 2–3 unbranched and 6½–7½ branched anal‐fin rays, and 37–40 lateral line scales are other morphological characteristics of C. muscatense. C. muscatense is also well distinguished by molecular characters among its congeners. The first molecular phylogenetic analysis of the genus, covering all currently recognized Cyprinion species except for C. watsoni, is also presented. C. muscatense is resolved as the sister species to another endemic fish of the Arabian Peninsula Cyprinion mhalense, with a Kimura‐2‐Parameter model distance of 5.3%. [ABSTRACT FROM AUTHOR]

Climate change is expected to affect freshwater water bodies worldwide, especially those located in semiarid and arid regions, including the Arabian Peninsula. Species distribution modeling has been widely used to predict the effects of climate changes on aquatic species. Occurrence records of the cichlid fish Nile tilapia, Oreochromis niloticus, were geographically mapped, followed by the implementation of species distribution models to delineate its range within the sensitive inland water system of the southeastern Arabian Peninsula. The analysis encompassed the examination of species presence data in the context of environmental variables, leading to the development of an ensemble model for habitat suitability, combining four distinct species distribution models. The findings indicated that the mean diurnal range and precipitation seasonality emerged as the most influential factors in predicting the suitability of habitats for O. niloticus. The response curve analysis indicated that the presence probability of O. niloticus decreased with increasing mean diurnal range and decreasing precipitation seasonality. The suitable distribution ranges for O. niloticus in the studied area were mainly distributed in the northeast of this region, where native/endemic fish diversity is high. The ensemble model results specified a significant impact of climate change on O. niloticus distribution, so highly suitable areas for this species will be reduced, while areas with low to moderate suitability increase slightly or remain unchanged. While O. niloticus is anticipated to display resilience and prosper under the influence of climate change, it remains paradoxical that its habitats are at risk of being compromised by climate-induced alterations. Consequently, even this resilient species stands susceptible to the repercussions of climate change. Due to the worldwide severe impacts of Nile tilapia, regular monitoring of freshwater ecosystems and fish fauna—especially in the northeast of the Arabian Peninsula, which has currently been invaded by this alien species—and protecting the region from key anthropogenic stressors are recommended to successfully conserve the freshwater fishes, which include about 22 recognized fish species in 16 genera, 10 families, 7 orders, and a class including 20 natives (7 endemic) species, out of which 13 species co-occur in sympatricity with O. niloticus. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Having parts of three freshwater ecoregions, i.e., Oman Mountains, Southwestern Arabian Coast, and Arabian Interior, Oman is considered to have the greatest freshwater biodiversity among the Arabian Peninsula countries. Freshwater habitats and biodiversity of Oman are unique and greatly valued for the crucial role they play in people's survival, as well as that of its native/endemic biota. An obvious starting point and fundamental step to conserve biodiversity and implementing planning management strategies is correct identification and delineating of the taxonomic and conservation units, and their distribution ranges especially endemic and native faunal elements including small, colorful, and mosquito-eating fish species of the genus Aphaniops. Five species of Aphaniops are present in the northern marginal basins of the Indian Ocean, however, there is still a lack of distributional and taxonomic data in many parts, and the species have not been studied yet for their phylogeographic and population structures, which are essential in designing habitat management and conservation plans. This study analyses mitochondrial COI data of Aphaniops samples collected from numerous widespread localities in Oman, a rarely studied area for this group, using a phylogenetic and phylogeographic framework. Our results confirm the presence of two species in Oman, A. kruppi and A. stoliczkanus, revise and suggest wider distributional ranges for both species, and suggest that A. kruppi is represented by two northern and one southern management units, while A. stoliczkanus is divided into two evolutionary units worthy of additional taxonomic evaluation. [ABSTRACT FROM AUTHOR]