Impact of Natural Disaster and Essential Spawning Habitat (ESH) Characteristics on the Conservation of the Vulnerable Endemic Bilih Fish (Mystacoleucus padangensis) in Lake Singkarak, Indonesia

Abstract

The Bilih fish (Mystacoleucus padangensis) is a high value endemic species critical to regional aquaculture biosystems. Currently listed as Vulnerable (VU) on the IUCN Red List, its wild stocks are facing an acute ecological and economic crisis, evidenced by a dramatic 99% collapse in catch volume (from 1 ton/day in 2002 to only 10 kg/day in 2025). This study aimed to characterize the Essential Spawning Habitat (ESH) and governing reproductive strategies, and to develop conservation management principles. Environmental metrics and habitat characteristics (substrate, depth) were measured. Results confirmed that the ESH functions as a critical biosystem component, defined by extremely shallow waters (4–16 cm) and sandy and rocky substrates. Precise environmental cues, specifically consistently low nocturnal temperatures (22–24°C), act as triggering inputs for migration and spawning. This existing stock crisis was severely exacerbated by a catastrophic flood and landslide event that occurred on November 27, 2025, in the spawning locality of West Sumatra. The disaster resulted in the critical degradation of the ESH, primarily through infilling the original substrate with unsuitable mud and fine sand. This damage effectively eliminated the essential rocky spawning media required for behavioral triggering, consequently disrupting the remaining reproductive cycle and accelerating the failure of current resource management efforts. Given the evident high sensitivity of the reproductive process to specific biosystem inputs and the physical destruction of the ESH by the natural disaster, this study urgently recommends strict conservation zoning and ecology based management. Crucially, these must be immediately followed by habitat restoration efforts to reinstate the necessary rocky substrate. Such measures are vital inputs for the regional biosystem, not only to prevent the immediate loss of this Vulnerable endemic germplasm but also to secure the biological foundations required for future resource recovery and sustainable ex-situ aquaculture development.