The complete mitochondrial genome and phylogenetic position of Schizothorax argentatus (Cyprinomorpha: Crypriniformes: Cyprinidae).

We investigated the vulnerable fish species Schizothorax argentatus Kessler, 1874, using low-coverage whole genome sequencing data. The assembled 16,587 bp mitochondrial genome has a nucleotide composition of A = 29.8%, T = 25.3%, G = 17.9%, and C = 27.0%, containing 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes with a gene arrangement identical to other cofamilial species. Phylogenetic analyses of 71 schizothoracine fishes suggest a close relationship between S. argentatus and Schizothorax eurystomus, sharing a common ancestor with Schizothorax pseudoaksaiensis. Our study supports dividing extant schizothoracine fishes into two tribes, Schizothoracini and Schizopygopsini. The estimated time to most recent common ancestor (tMRCA) and their distribution imply geological and climatic events during the Miocene around the Qinghai-Tibet Plateau as significant evolutionary drivers explaining the diversification of main clades in schizothoracine fishes.

Diet Diversity of the Fluviatile Masu Salmon, Oncorhynchus masou (Brevoort 1856) Revealed via Gastrointestinal Environmental DNA Metabarcoding and Morphological Identification of Contents.

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.