The vital role of the gut microbiota in fish growth, development, immunity, and health has been largely confirmed. However, the interaction between environmental microbiota and the gut microbiota of aquaculture species remains unclear. Therefore, we analyzed the gut microbiota of largemouth bass (Micropterus salmoides) collected from subtropical ponds in southern China, as well as the pond water and aquatic sediment microbiota, using high-throughput sequencing of the 16S rRNA gene. Our results demonstrated significant differences in the compositions of pond water, sediment, and the gut microbiota of largemouth bass. Moreover, these compositions changed throughout the culture period. Only approximately 1% of the bacterial species in the pond sediment and gut microbiota were exchanged. However, the bacterial proportion of the gut microbiota from pond water microbiota was approximately 7% in samples collected in June and August, which increased markedly to 73% in October. Similarly, the proportion of bacteria in the pond water microbiota from the gut microbiota was approximately 12% in June and August, which increased to 45% in October. The study findings provide basic information for understanding the interactions between environmental microbiota and the gut microbiota of cultured fish, which may contribute to improved pond culture practices for largemouth bass.

In this study, microplastics in the surface water in the Pearl River Delta during different seasons were studied to analyze their temporal and spatial distribution, morphological characteristics, related socio-economic indicators, and potential ecological risks. Based on an analysis of surface water samples from 13 sampling sites, we found that the temporal and spatial distribution of microplastics in the Pearl River Delta were unbalanced. The microplastic abundances at the Qingqi, Chencun, Zuotan, and Beijiao sites were tremendously higher than those at other sites. Nevertheless, the abundance of microplastics at most sites was tremendously higher in the rainy season than dry season. Meanwhile, the morphological characteristics of microplastics had a strong correlation with the changes of season and site location. During the rainy season, the major color, shape, and size distribution of microplastics were gray (38.64%), strip (78.29%), and 100–500 μm (57.38%), respectively. The most usual color, shape, and size distribution of microplastics in the dry season were black (38.64%), granular (78.29%), and 0–100 μm (70.29%), respectively. As for the socio-economic indicators, including the degree of afforestation as well as the extent of industrial, transportation, and other human activities, all had varying degrees of impact on microplastic abundances. The potential ecological risk assessments demonstrated that most sites in the Pearl River Delta had a high potential for ecological risk related to microplastic pollution, which should be given more attention in the future. In summary, our investigations offer a theoretical basis for research related to microplastics in the Pearl River Delta and can further improve our understanding of the need to protect aquatic environments by exploring the overall ecological risks posed by microplastics.

Water pollution can be monitored through the use of indicator species, including Brachionus calyciflorus. To do this, it is necessary to understand the species’ population ecology. Four surveys of zooplankton were conducted in May, August, and December 2018 and February 2019 in the Pearl River Delta, China, to examine the population characteristics of B. calyciflorus. The temporal and spatial distribution of abundance, biomass, dominance, and occurrence frequency were compared with those from 2012 to investigate the relationship between changes in the population of B. calyciflorus and environmental factors. The average abundance, dominance, and occurrence of B. calyciflorus in this survey were significantly higher than those of 2012 in all seasons. Principal component analysis showed that environmental factors such as the temperature, transparency, total nitrogen, and total phosphorus of water had a major impact on the abundance of B. calyciflorus. There was a significant positive correlation with transparency, total nitrogen, and total phosphorus of water, and a very significant positive correlation with water temperature. Overall, these results demonstrated that the distribution characteristics of B. calyciflorus can reflect pollution in water bodies and can be used to evaluate water quality. These research results provide a reference for evaluating China’s river health and can help to manage water quality in the Pearl River Delta.