Microplastics are environmental contaminants and an emergent concern. Microplastics are abundant in freshwater and can cause biochemical stress in freshwater organisms. In the current study, rare minnows (Gobiocypris rarus) were exposed to 1μm polystyrene microplastics at 200 μg/L concentration. We observed various sublethal effects after four weeks of exposure but no mortality. Numerous cellular and tissue alterations were observed in the liver. Differential metabolites and differentially expressed genes between control and exposure groups were identified and mapped to pathways in the Kyoto Encyclopedia of Genes and Genomes. The combination of transcriptomic and metabolomic analyses revealed significantly varied metabolic pathways between the two groups. These pathways were involved in glucolipid, amino acid, and nucleotide metabolism. Results demonstrated that MP exposure induced immune reaction, oxidative stress, and disturbed glycolipid and energy metabolism. The current study provided novel insights into the molecular and metabolic mechanisms of microplastic ecotoxicology in rare minnow.

Microplastics are ubiquitous in the natural environment, especially in waters, and their potential impact is also a key issue of concern. In this study, we used 1 µm, 1000 μg/L, polystyrene (PS-MPs) particles to analyze the effects after exposure for 14 and 28 days in rare minnow (Gobiocypris rarus). Results indicated that PS-MPs induce structural alterations in the intestinal tissue, including epithelial damage, villi damage and the inflammatory cell infiltration, while the changes were severer after exposure for 28 days. Polystyrene microplastics also significantly increased the activities of catalase (CAT, increased 142 % and 385 % in 14d and 28d), superoxide dismutase (SOD, increased 17.76 % and 23.43 % in the 14d and 28d) and the content of malondialdehyde (MDA, increased 14.5 % and 442 % in the 14d and 28d), glutathione (GSH, increased 146 % and 298 % in the 14d and 28d). The results not only showed the characterization of gut microbial communities in rare minnow, but also indicated that microbial diversity and composition were altered in gut of fish exposed to PS-MPs. In the control groups, Proteobacteria (31.36-54.54 %), Actinobacteriota (39.99-52.54 %), Fusobacteriota (1.43-1.78 %), Bacteriadota (0.31-0.57 %) were the four dominant bacterial phyla in the intestinal of rare minnow. After exposure to microplastics, In the gut microbiota, the proportion of Proteobacteria increased 9.27 % and 30 % with exposure time, while Actinobacteria decreased 37.89 % and significantly different after 28 days. In addition, metabolomic analysis suggested that exposure to PS-MPs induced alterations of metabolic profiles in rare minnow and differential metabolites were involved in energy metabolism, inflammatory responsible secretion, oxidative stress, nucleotide and its metabolomics. In conclusion, our findings suggest that long-term exposure to microplastics could induce intestinal inflammation, oxidative stress, microbiota dysbiosis and metabolic disorder in rare minnow, and the alterations and severity were exacerbated by prolonged exposure. This study has extended our cognition of the toxicity of polystyrene, and enriched theoretical data for exploring the toxicological mechanism of microplastics.

Environmental enrichment is a method to increase environmental heterogeneity, which may reduce stress and improve animal welfare. Previous studies have shown that environmental enrichment can increase the growth rate, decrease aggressive and anxiety-like behaviors, improve learning ability and agility, and reduce cortisol levels in animals. These effects usually differ between species. Unfortunately, habitat enrichment on laboratory fish is poorly studied and seldom adopted in care guidance. Rare minnows (Gobiocypris rarus) have been cultured as a native laboratory fish in China in barren banks without environmental enrichment since 1990; they have been widely used in studies on ecotoxicology, environmental science, and other topics. The purpose of this study was to investigate the effect of environment enrichment on the growth, physiological status, and anxiety-like behavior of laboratory rare minnows. We observed and analyzed SGR, cortisol levels, DA, DOPAC, 5-HT and 5-HIAA, and anxiety-like behavior indexes after one month of treatment in barren (control) and enrichment tanks. We found that there were no significant differences in SGR, anxiety-like behavior, DA, DOPAC, or 5-HIAA levels between the two treatments. However, higher cortisol and 5-HT levels were observed in the enrichment tanks. This study suggests that rare minnows might be influenced by their living environment, and future related studies should consider their environmental enrichment.

The river–reservoir transitional zones play an important role in maintaining riverine fish biodiversity and abundance in highly regulated rivers. The Upper Yangtze River, which contains 286 fish species, is experiencing intense hydropower development. However, few studies have been conducted on the spatial distribution of fish in the river–reservoir transitional zones in the Upper Yangtze River, and it is therefore difficult to predict how this development will impact the region. In this study, a 200-kHz split-beam acoustic system in combination with biological samplings was used to investigate the composition and spatiotemporal distribution of the fish in the transition zone of the Three Gorges Reservoir (TGR) in 2017. The biological samplings comprised 7434 individuals from 61 species, 38 genera, 15 families, and 5 orders. The dominant fish species were Rhinogobio cylindricus, Coreius guichenoti, Hemiculter bleekeri, and Pelteobagrus vachelli. Acoustic detection identified the mean target strength (TS) to be −55.6 in May, −57.8 in August, and −55.8 dB in December. Accordingly, the average fish density was 4.96, 6.96, and 4.42 ind/1000 m³. Significant differences were found in the TS and fish density between flood season (August) and non-flood season (May and December). Spatially, fish preferred the meandering sections at 10–20 m deep. A size-dependent vertical distribution pattern was observed, with larger fish in the deeper layers and smaller fish in shallower waters. Lastly, our results suggest that meandering deep channels should be assigned high priority with respect to fish conservation in the Upper Yangtze River.

Understanding energy flow and nutrient pathways is crucial to reveal the dynamics and functions of riverine ecosystems and develop appropriate conservation strategies. In this study, we utilized stable isotopes of δ¹³C and δ¹⁵N to examine the fundamental characteristics of trophic position, trophic niche, and carbon source for the food web in the midstream of the Chishui River, a tributary to the Yangtze River. Our results showed that stable isotope signatures among different sorts of basal resources and consumers were significantly distinguishable and that the food chain consisted of four trophic levels, indicating the multiple trophic pathways and long food chain length here. The trophic guilds of fish were classified into four categories, in which herbivorous and carnivorous fish showed greater trophic diversity and omnivorous fish had higher trophic redundancy, which meant that there was a stable trophic niche structure in the study area. Phytoplankton and periphyton presented the largest contributions to consumers, indicating that autochthonous productivity was the dominant carbon source in the midstream of the Chishui River. Since the Chishui River is still in a natural condition without any dam constructions, the autochthonous productivity, stable trophic niche structure, multiple trophic pathways and long food chain length found here demonstrate its high conservation value. Therefore, the strategy to refrain from damming on this river should persist into the future.