Lake Ulungur, located in the desert region of northwest China, is one of the most important fishing grounds in the Chinese inland area. Ulungur possessed a simple fish assemblage of 7 indigenous species of fish, dominated by the common perch, Perca fluviatilis Linnaeus and Leuciscus dzungaricus. Over the last 40 years, 14 non-indigenous species of fish have been introduced into this fragile ecosystem via intentional or unintentional human activities. Over the decades since these introductions, the fish community of Ulungur has been severely altered. Most of the niches that had inhabited by the native species of fishes are now occupied by these non-native species. The two, once dominate species, the common perch and Leuciscus dzungaricus, have become endangered and threatened with extinction, while the non-native Pond smelt (Hypomesus olidus Pallas), the Aral bream (Abramis brama orientalis Berg) and the Northern pike (Esox lucius Linnaeus), have become the most prevalent species. In this paper, non-indigenous fish introductions and the corresponding changes in native fish communities in Ulungur are outlined. Possible mechanisms of community succession were analyzed to provide information for the management of fish introduction.

Hypomesus nipponensis a commercially valuable fish within the Osmeriformes order, is naturally found in northeastern Asia and has been extensively introduced for commercial purposes across eastern Asia. To investigate the taxonomic status and evolutionary history of Hypomesus nipponensis within the Osmeridae family, we first performed a de novo genome assembly using PacBio HiFi reads and CLR (Continuous Long Read) reads. Subsequently, we leveraged synteny information from closely related species to further refine the assembly and construct a chromosome-level genome. The final assembly spans 507.8 Mb, with a scaffold N50 of 20 Mb, achieving chromosome-level contiguity. It comprises 164 Mb of repetitive sequences and encodes 27,876 protein-coding genes. Compared to previous assembly, the H. nipponensis genome is notably more contiguous and complete. Notably, it contains an unusually high proportion of tandem repeats, which likely contributed to the assembly challenges encountered in earlier efforts. We also observed the transposons of H. nipponensis have expanded significantly in recent times, and paralogous gene families have expanded during the same period. Our analysis estimates that H. nipponensis, Osmerus eperlanus, and Hypomesus transpacificus diverged from a common ancestor approximately 24.1 million years ago, with significant chromosomal segment recombination events occurring during their divergence. Additionally, we compared the genomes of O. eperlanus and Hypomesus and found that most of the genes in the Presence/Absence Variants (PAVs) of O. eperlanus were associated with immune response. Our efforts significantly enhance the genome’s integrity and continuity for this ecologically and commercially important fish, providing a chromosome-level genome draft that supports fundamental biological research while offering insights into the evolutionary relationships and genomic diversity within the Osmeriformes order. This advancement has profound implications for understanding the evolutionary history and adaptive strategies of H. nipponensis.

Ontogenetic niche shifts have played an important role in the life history and ecological functions of fish. The clearhead icefish (Protosalanx chinensis, Basilewsky, 1855) is a small, pelagic, and commercially important fish that mainly feeds on zooplankton and will transition to feeding on fish when prey fish are available, though its life span is only about one year. In fact, we know little about the food selectivity and diet shifting of P. chinensis before its transition to feeding on fish. To reveal the food selectivity of P. chinensis before its transition to feeding on fish, the gut contents and environmental zooplankton community were investigated simultaneously in Lake Dalong of Northeastern China from April to June 2021. The results showed that P. chinensis experienced a diet shift from copepoda to cladocera during spring in Lake Dalong. From April to early June, both the size of cladocera and copepoda in guts increased as the size of P. chinensis increased. However, the favorite category changed to the smaller cladocera in late June, when the density of the smaller cladocera was rather high relatively. Considering June was the critical period for P. chinensis to prepare for transitioning to feeding on fish, the food resources availability must be seriously considered for sustainable aquaculture of P. chinensis. It was hypothesized that there was a trade-off of feeding selectivity between the size and density of the prey.