Molecular identification and temporal genetic differentiation of Cyprinus carpio (Cypriniformes: Cyprinidae) eggs attached on artificial fish nests

Reproductive isolation by time can occur in fish populations composed of individuals with different reproductive schedules. Most studies have tested this phenomenon using mature fish rather than their offspring, which may mask signals of population relationships. We directly sampled fish eggs from artificial fish nests at four different time instances and subsequently fed the eggs to fish larvae in an indoor laboratory. Fish larvae, of each timeline, were randomly selected for species identification using the mitochondrial cytochrome c oxidase I (COI) gene and performed population analyses utilizing the concatenated sequences of COI gene and the mitochondrial control region (D-loop). Neighbor-joining tree and Automatic Barcode Gap Discovery (ABGD) using COI sequences showed that all analyzed larvae can be assigned to the common carp (Cyprinus carpio). Significant differentiation among four demes inferred from the evidence of the concatenated sequences indicated temporal structuring in C. carpio demes within a reproductive season. Haplotype networks and a Bayesian method in BAPS also detected signals of population differentiation among the four demes. The pattern observed in C. carpio demes revealed the reproductive strategy of the species and provided knowledge allowing establishment of conservation units.