Masu salmon, Oncorhynchus masou (Brevoort 1856), a commercially important fish species endemic to the North Pacific Ocean, attained national second-level protected animal status in China in 2021. Despite this recognition, knowledge about the trophic ecology of this fish remains limited. This study investigated the diet diversity of fluviatile Masu salmon in the Mijiang River, China, utilizing the gastrointestinal tract environmental DNA (GITeDNA) metabarcoding and morphological identification. The results revealed a diverse prey composition, ranging from terrestrial and aquatic invertebrates to small fishes. The fluviatile Masu salmon in general consumed noteworthily more aquatic prey than terrestrial prey. There were much more prey taxa and a higher diet diversity detected by GITeDNA metabarcoding than by morphological identification. GITeDNA metabarcoding showed that larger and older Masu salmon consumed significantly more terrestrial insects than aquatic prey species did, with 7366 verses 5012 sequences in the group of ≥20 cm, 9098 verses 4743 sequences in the group of ≥100 g and 11,540 verses 729 sequences in the group of age 3+. GITeDNA metabarcoding also showed size- and age-related diet diversity, indicating that the dietary niche breadth and trophic diversity of larger and older Masu salmon increased with food resources expanding to more terrestrial prey. Terrestrial invertebrates of riparian habitats play a vital role in the diet of fluviatile Masu salmon, especially larger individuals, highlighting their importance in connecting aquatic and terrestrial food webs. Conservation plans should prioritize the protection and restoration of riparian habitats. This study advocates the combined use of GITeDNA metabarcoding and morphological observation for a comprehensive understanding of fish diet diversity.

Chitons (Mollusca: Polyplacophora) are a relatively primitive group within Aculifera that have retained their past life history and ecological traits. While chitons are recognized for their evolutionary significance and societal value (e.g., food, medicine, biomimetics), key aspects of their phylogeographic patterns and microevolutionary processes remain poorly understood, particularly regarding spatial dispersal and adaptation to the challenging intertidal zone environment. Here we show a population genomic analysis of the Chinese chiton (Liolophura sinensis), a species recently delineated from the Liolophura japonica species complex. Using high-depth resequencing of 68 individuals across nine populations, we identify distinct genetic substructure between the Taizhou and southern groups, with divergence dating back to approximately 19.0 thousand years ago, a timing that overlaps with late Pleistocene sea-level minima. A unidirectional gene flow pattern indicates ocean current-mediated larval dispersal, which is consistent with species-specific life history traits. Moreover, selection scans reveal significant enrichment of genes associated with immune responses, cellular homeostasis, and cytoskeleton dynamics, all traits that are potentially relevant for survival in wave-exposed rocky habitats. Our analyses identify strong population structure, recent divergence, and genomic regions potentially associated with local environmental variation, providing a foundational framework for future research on adaptation in marine intertidal species.