Scanning electron microscopy and morphometric analysis of the tongue in four carnivorous fish species—Dusky Grouper (Epinephelus marginatus), John Dory (Zeus faber), Squirrelfish (Sargocentron spinosissimum), and Red Lionfish (Pterois miles)

Abstract

The Mediterranean Sea is home to a wide variety of fish species that exhibit carnivorous behavior, particularly during the juvenile to pre-adult stages. This study aimed to compare the tongue morphology of four Mediterranean carnivorous fish species: the dusky grouper fish (Epinephelus marginatus), John Dory fish (Zeus faber), squirrelfish (Holocentrus spp.), and red lionfish (Pterois volitans). To our knowledge, no previous studies have conducted a comparative analysis of tongue morphology among these species, an important area of investigation for understanding species-specific adaptations related to feeding behavior, prey capture mechanisms, and ecological niches. We examined morphometric parameters, gross anatomical features, and scanning electron microscopic (SEM) characteristics of the dorsal tongue surface. Among the species studied, the John Dory fish had the highest body depth-to-length ratio (38.8 %), while the squirrelfish showed the highest eye diameter-to-head length ratio (12.2 %) and the red lionfish the lowest (3.04 %). The dusky grouper fish exhibited the highest tongue-to-body length ratio. In contrast, the red lionfish had a shorter tongue with a broad root nearly equal in size to the tongue itself. All species had triangular tongues, but only the red lionfish showed a constriction before the apex. The tongue apex differed among species: it was rounded in the dusky grouper, pointed in both the squirrelfish and red lionfish, and featured a distinct structure in the John Dory fish. The dorsal tongue surface exhibited species-specific features, including elevations, ridges, grooves, and unique apical structures. SEM analysis revealed microridges, folds, multiple papilla types, and taste buds. The dusky grouper displayed volcano-shaped taste buds and circumvallate papillae; the John Dory fish showed rosette-shaped protrusions and circumvallate-like papillae; the squirrelfish had scale-like and dome-shaped papillae; and the red lionfish revealed elliptical and dome-shaped structures with microgrooves and mucus secretion. In conclusion, variations in tongue morphology and its macro- and microstructures likely reflect differences in prey type, feeding behavior, and ecological adaptation, and this study lays the groundwork for future comparative research on Mediterranean fish.