Otolith-based species identification in the killifish Aphaniops (Teleostei; Cyprinodontiformes; Aphaniidae) using both morphometry and wavelet analysis

Abstract

The killifish genus Aphaniops consists of nine species distributed in Eastern Africa and the Middle East. However, distinguishing these species from each other based on morphological traits is challenging. Here we investigate the utility of otoliths (sagittae) in distinguishing between A. dispar, A. ginaonis, A. hormuzensis, A. kruppi and A. stoliczkanus. Our approach is based on otoliths from 89 specimens and involves (1) otolith morphometrics, following prior recommendations, (2) shape analysis of otolith contours based on discrete wavelet transformation—a novel method in killifish otolith research—and comparative statistical analyses. Both methods reveal significant interspecific variation in the otolith regions of the rostrum, antirostrum and excisura. While method (1) effectively discriminates most species, method (2) struggles to differentiate A. hormuzensis, A. stoliczkanus and A. kruppi. Additionally, both methods encounter challenges in correctly classifying A. hormuzensis due to the high otolith variability of this species in our sample. Possible factors accounting for their variability are environmental fluctuations at the sampled hot sulphuric spring (Khurgo) and potential introgressive hybridization. We conclude that otolith morphometry is a valuable tool for Aphaniops species identification. Furthermore, we found that the distinctiveness of species-specific otolith traits increases with the divergence age of the species.