Riverbed Substrate Requirements for Natural Reproduction of Gymnocypris przewalskii

SIMPLE SUMMARY: Riverbed substrate plays a vital role in the growth, reproduction, predation of fish as an important aspect of a river ecosystem. This research represents the first systematic examination of the riverbed substrate requirements for the natural reproduction of Gymnocypris przewalskii through artificial simulation and spawning ground substrate transformation experiments. Results showed that pebble was an indispensable factor for the reproduction of Gymnocypris przewalskii and the increase of pebble had an obvious promoting effect on the reproduction. The findings of this study could provide guidance for the wild population recovery, artificial reproduction, and restoration of natural spawning grounds of this fish species. ABSTRACT: Gymnocypris przewalskii (i.e., Qinghai Lake naked carp) is a migratory fish species that lives in highland brackish water. It is important to understand the abiotic environment required by this fish to reproduce naturally so that its habitat can be protected and the wild population can be conserved. Here, artificial simulation and spawning ground substrate transformation experiments were conducted to examine the riverbed substrate requirements for G. przewalskii to naturally reproduce. Using various techniques (in vitro markers, videography, and Ethovision XT behavior tracking), this study systematically investigated the riverbed substrate preferences of G. przewalskii as well as the characteristics and effectiveness of natural reproduction induced by pebble riverbed substrate. The findings can be summarized as follows: (1) the habitat preferences of G. przewalskii differed significantly between various riverbed substrate, with pebble substrate being preferred during natural reproduction, and sand substrate being preferred pre- and post-spawning, and (2) the natural reproduction of G. przewalskii was heavily reliant on pebble riverbed substrate. Specifically, pebble substrate significantly improved spawn quantity and fertilization rate. These findings provide scientific evidence for the improvement and restoration of G. przewalskii spawning grounds, and insights regarding the artificial bionic reproduction of G. przewalskii.