New Record of the Mediterranean Killifish <scp> <i>Aphanius fasciatus</i> </scp> in Croatia—Phylogenetic and Morphological Profile of the Population With Conservation Recommendations

ABSTRACT The Mediterranean killifish, Aphanius fasciatus , is an euryhaline species that inhabits aquatic habitats characterized by extreme physiochemical parameters, such as salinity and temperature. Previously, seven populations of A. fasciatus were recognized in Croatia. The distribution range of this species is highly fragmented, with all previously recorded sites being isolated from one another due to the limited number of suitable habitats. This study reports the presence and status of a new population of A. fasciatus on the Istrian Peninsula in Croatia. The objectives of this study were to describe the morphological characteristics and genetic diversity of the population in the Šćuza Bay, determine the phylogenetic position and relatedness to other populations and propose conservation measures for the survival of the population. To determine the phylogenetic relationships among populations, a phylogenetic reconstruction was performed based on cytochrome b gene sequences using the maximum parsimony, maximum likelihood, Bayesian inference and median‐joining methods. In addition, population viability analysis was conducted to determine which threats have the greatest effect on population survival. The results place the studied population of A. fasciatus within the northern Adriatic group. A moderate genetic diversity was found, somewhat higher than in other populations on the eastern Adriatic coast. Habitat degradation (such as filling up and covering the coast and the seafloor with solid material and wastes) was identified as the greatest threat to the survival of the population.