Environmental DNA dynamics during embryonic development in the rare minnow Gobiocypris rarus

Understanding environmental DNA (eDNA) dynamics in the major developmental stages of fish species is fundamental for developing eDNA methods to aid conservation and management of fish species and/or populations. In this study, we used the model fish species, the rare minnow (Gobiocypris rarus), to assess the temporal changes of its mitochondrial and nuclear eDNA concentrations during its embryonic development in a culture dish experiment. Mitochondrial cytochrome b (Cytb) and nuclear internal transcribed spacer-1 (ITS1), considered as representative DNA fragments, were amplified by quantitative PCR (qPCR). In this embryo culture trial, spikes in mitochondrial (mt-) and nuclear (nu-) eDNA concentrations were found just after egg fertilization and after embryo hatching, and a modest but positive relationship was found between the eDNA concentration and the number of hatched individuals, illustrating eDNA may be used to monitor the spawning and hatching events of externally fertilizing fishes. These findings provided basic information on eDNA dynamics during fish embryonic development and a new insight to design eDNA methods to monitor early developmental stages of fish species.