Cryptic biodiversity in Australian freshwater fishes
The resolution of cryptic species diversity within H. klunzingeriaccords with the trend of finding new candidate species in Australian freshwater fish guided by molecular data (e.g., Adams et al., 2014; Hammer et al., 2019; Unmack et al., 2022). Such data can not only reveal the presence of cryptic species but can also uncover nuanced evidence for admixture and introgression that was often not detectable prior to the advent of detailed genomic datasets and the coupling of ordination and tree-based approaches. The application of this modern molecular approach to taxonomic uncertainty in H. klunzingeri has identified the presence of additional candidate species in this nominal taxon. Moreover, as in our companion study of Australian smelt (Retropinna spp.; Unmack et al., 2022), additional morphological, phenotypic or ecological data are not required in most cases to validate the identified candidate species per se (the exceptions being KW+ versus KS in Hypseleotris , and COO versus MTV inRetropinna ). However, such data remain the foundation for formal description and naming of candidate species and are of course valuable for addressing other questions about the biology of individual species, whether formally named or not.