Simple SummaryThis study explained the effects of the type and abundance of micro-topography in a river basin on the geographical distribution of the endemic fishPseudopungtungia tenuicorpa. This species was found to preferentially select cracks as its spawning habitat, followed by the nests of other fish. In particular, cracks smaller than 5 cm provided a safe area for the spawned eggs while being difficult for other fish to invade.P. tenuicorpaeggs spawned in cracks larger than 6 cm were continuously consumed or damaged by other predatory fish. In South Korea, cracks smaller than 5 cm are more abundant in the upstream parts of the Han River than in other river basins (Geum River and Nakdong River), hence explaining the limited spatial distribution ofP. tenuicorpa.AbstractIn this study, we hypothesized that the limited geographical distribution ofPseudopungtungia tenuicorpain South Korea is closely related to the local abundance of their preferred spawning habitats. Eggs ofP. tenuicorpawere most frequently observed in cracks smaller than 5 cm, followed by the nests of other fish, such asCoreoperca herzi. Although eggs ofP. tenuicorpawere also found in cracks larger than 6 cm, most of them were consumed or damaged by other fish. However, the number ofP. tenuicorpaeggs spawned in cracks smaller than 5 cm remained similar to the number of eggs at the time of initial spawning, even after 9 days. The strong preference ofP. tenuicorpafor cracks smaller than 5 cm was found to influence the geographical distribution ofP. tenuicorpain South Korea. In the upper reaches of the Han River, the ratio of cracks smaller than 5 cm is higher than that in the Geum River and in the Nakdong River, which contributes to the stable population growth ofP. tenuicorpathere. In the future, management strategies to maintain/restore cracks smaller than 5 cm should be reviewed for the preservation of this endemic fish in South Korea.