﻿Occurrence of contact organs and sexual dimorphism in fishes of the family Profundulidae (Actinopterygii: Cyprinodontiformes)

The family Profundulidae is one of the few families of freshwater fishes endemic to the Mesoamerican region, and one of the least speciose within the order Cyprinodontiformes, with only 13 valid species. Sexual dimorphism is poorly developed and sparsely studied in this family. Herein, we report the presence of spicule-like organs of contact in scales and fins (anal and dorsal) in fishes of the family Profundulidae and discuss the use of spicules as a means to facilitate the identiﬁcation of male and female in this family. Data from museum specimens of the 13 species of profundulid fishes were analyzed. We studied the following species: Tlaloc labialis (Günther, 1866); Tlaloc candalarius (Hubbs, 1924); Tlaloc hildebrandi (Miller, 1950); Tlaloc portillorum (Matamoros et Schaefer, 2010); Profundulus punctatus (Günther, 1866); Profundulus guatemalensis (Günther, 1866); Profundulus oaxacae (Meek, 1902); Profundulus balsanus Ahl, 1935; Profundulus kreiseri Matamoros, Schaefer, Hernández et Chakrabarty, 2012; Profundulus parentiae Matamoros, Domínguez-Cisneros, Velázquez-Velázquez et McMahan, 2018; Profundulus mixtlanensis Ornelas-García, Martínez-Ramírez et Doadrio, 2015; Profundulus adani Dominguez-Cisneros, Velázquez-Velázquez, McMahan, et Matamoros, 2021; Profundulus chimalapensis Del Moral-Flores, López-Segovia et Hernández-Arellano, 2020. Scales were observed and photographed with a Hitachi VP-MEB SU1510 scanning electron microscope; the spicules in fins were observed from specimens cleared and double-stained. This study revealed the presence of 1–10 spicules on the surface of the scales in males and its absence in females of all species analyzed. Numerous, small and thin spicules were also observed and they were restricted to the middle rays of the anal and dorsal fins of the males. The observation of spicules in the anal fins for the sexual identification of profundulid fishes constitutes an advantage of operational simplicity, speed, and potential for its application in taxonomic and ecological studies.