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.

Information about the population structure, including the age and sex composition, growth characteristics, and diet of fish, is essential for the conservation and sustainable exploitation of fish stock. The burbot, Lota lota, is the only freshwater species of the family Lotidae in the Amur (Heilongjiang) River catchment located in northeastern China. Information on the biological characteristics and data on the population structure of this fish from the Amur River are scarce. To study these factors in burbot, Lota lota, in the Amur River of China, 749 specimens from four sampling areas were taken and analyzed in October 2022, January 2023, and May 2023. The ages of the sampled fish ranged from 1+ to 7+ years. The female/male ratio was 1.04:1, and body length and mass varied from 175 to 595 mm and 73.5 to 1958.7 g, respectively. The length–weight regression parameter b value was estimated as 2.80. The parameters of the von Bertalanffy growth model were L_∞ = 596, K = 0.221, and t₀ = −0.771 for all sampled fish; L_∞ = 625, K = 0.208, and t₀ = −0.756 for females; and L_∞ = 584, K = 0.219, and t₀ = −0.980 for males. The analysis of the stomach contents showed fish to be the major source of nutrition across all areas and sampling periods. In January, the secondary prey of burbots in the Huma reach of the upper Amur River was aquatic insect larvae, while, in the Tongjiang and Fuyuan reaches of the middle Amur River, the secondary prey was shrimp. The mean stomach fullness index and rate of empty stomachs differed with the sampling area, with the greatest proportion of empty stomachs observed in the Luobei reach of the middle Amur River, and the lowest in the Tongjiang and Fuyuan reaches. The mean stomach fullness index showed the opposite trend. In the Huma reach, the contributions of fish to the diet and the mean stomach fullness index were significantly higher in May than in October and January. The study provides the first detailed information on the population age and sex structure, growth patterns, and feeding ecology of burbots from the Amur River, China. The results will aid in formulating management strategies and regulations for local populations of burbots in the Amur River, China.

To investigate the structure of phytoplankton communities and the ecological niches of dominant species in the middle and upper reaches of the Yarlung Zangbo River, we collected samples at 14 sites in April (spring) and September (autumn) 2023. A total of 198 phytoplankton species were identified belonging to 6 classes, 13 orders, 24 families, and 53 genera. The community structure was dominated by diatoms, green algae, and cyanobacteria. In April, 163 species of phytoplankton from four phyla were identified, with abundance ranging from 2.94 × 10⁵ to 2.32 × 10⁶ cells/m³ and an average of 1.28 × 10⁶ cells/m³. In September, the abundance of phytoplankton ranged from 1.52 × 10⁵ to 1.58 × 10⁶ cells/m³, with an average value of 6.76 × 10⁵ cells/m³. Sixteen species were classified as dominant (Y > 0.02), among which four showed dominance in both sampling periods, with their dominance level and niche width differing with the season. Water temperature increased with decreasing altitude. At 4500 m compared to other elevation ranges (>4500 m; 4000–4500 m; 3500–<4000 m; <3500 m). The effect of elevation on the community structure was greater than that of season. This is the first study to characterize the association of ecological niches of phytoplankton in the upper reaches of the Yarlung Zangbo River with physicochemical environmental parameters. This provides baseline information for the conservation of biodiversity and management of aquatic ecosystems in the rivers of the Tibetan Plateau.

This study investigated the fish species composition and environment of the Emur River, a tributary of the Upper Heilongjiang (Amur) River system, which is a typical extreme-cold region of China. From 2022 to 2024, 28 native species (27 species of fish and 1 species of lamprey), including 4 endangered species, were monitored from 14 sampling sites. When grouped according to the main stream vs. tributaries and summer vs. autumn, we found significant differences (p < 0.05) in the composition of the fish communities. In autumn, the main stream fish assemblage was dominated by common species that prefer a slow current, including Phoxinus phoxinus (33.7%), Lota lota (25.2%), and Phoxinus lagowskii (19.8%). The tributary fish assemblage was primarily composed of typical coldwater fish species, such as L. lota (48.9%), Cottus poecilopus (20.2%), and Thymallus grubii (18.1%). However, in summer, there was no significant difference between the main course and tributaries. Canonical correspondence analysis showed environmental factors, including water temperature, elevation, and dissolved oxygen, to have significant impacts on the fish distribution to an extent that varied with species. This study may contribute to the management of coldwater fish diversity in mountain rivers and the protection of aquatic species habitats in regions of extreme cold.

The stability of the ecosystem directly affects water quality and safety, fishery production, and people’s quality of life along the route. Therefore, a large amount of biological information on five dominant species of baitfish, including Hemiculter leucisculus, Acheilognathus macropterus, Rhodeus sericeus, Pseudorasbora parva, and Squalidus argentatus, was collected in the lower reaches of the Songhua River. The population parameters and variation rules of these fish were evaluated. The results showed that current exploitation of fish resources in the lower reaches of the Songhua River is excessive. The growth rate of baitfish is accelerating, but their growth potential is decreasing; the fish community structure is homogeneous, and the excessively small size of fish at a low age is obvious. In addition, the growth length coefficients of the five baitfish species were all greater than 0.2, which indicates fast growth; the growth performance indices were from 3.49 to 4.37. The exploitation rate of the Hemiculter leucisculus and Squalidus argentatus minnows was greater than 0.5, and the exploitation rates of all species except Pseudorasbora parva were higher than Emax. To ensure the size of the main baitfish populations in the lower reaches of the Songhua River, the mesh size of all nets should be controlled above 45 mm. In summary, these results provide a scientific basis for understanding the trend and growth of baitfish resources, identifying the distribution of major commercial or endangered fish feeding grounds in the region, and balancing ecosystem health integrity in the lower reaches of the Songhua River.

We evaluated growth, mortality, and resource utilization of burbot, Lota lota, in the upper reaches of Heilongjiang River, China. The population has experienced significant decline, and, despite substantial recovery, concerns regarding resource management have arisen. A total of 638 specimens collected from October 2022 to October 2023 were used to calculate the relationship between body length and weight, which ranged from 107 to 529 mm and from 8.91 to 1474.17 g, respectively. FAO FiSAT II software was used to estimate population parameters based on body length frequency distribution of the samples. The calculated progressive body length value and the growth coefficient were 551.25 mm and 0.16, respectively. The natural mortality rate of burbot is 0.31 a⁻¹. Assuming a total mortality rate of 0.41 a⁻¹, the estimated current exploitation rate is 24.39%. Total biomass (94.76 t) and maximum sustainable yield (14.69 t) were estimated based on length-structured virtual population analysis. Burbot, of the upper reaches of Heilongjiang River, is a fast-growing fish that is well-suited to the ecology of the investigated area. The current research yielded suggestions for utilization of resources to ensure the preservation of the species, as well as the development of the local economy.