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.

The trophic status of a reservoir in the southern subtropical region of China was evaluated by non-biological environmental factors from 2011 to 2020. The relationship between the community structure of planktonic rotifers and eutrophication was examined based on the species composition, dominant species, standing crop, and biodiversity index of the planktonic rotifers in the surface water. The results showed that the reservoir was continually slightly eutrophic. The dominant species of planktonic rotifers were mesosaprobic species such as Polyarthra trigla and Brachionus angularis. The overall abundance fluctuated between 438 and 1360 ind./L; biomass fluctuated between 520 and 1613 μg/L, and the biodiversity index fluctuated between 1.27 and 2.43. Redundancy analysis showed that chlorophyll a content, water transparency, total phosphorus, and water temperature had significant impacts on the abundance of planktonic rotifers. The results demonstrate a close relationship between the community structure of planktonic rotifers and eutrophication. In other words, eutrophication was the main cause of the changes in the community structure of planktonic rotifers in surface water.

The gut microbiota (GM) compositions of aquatic animals are influenced by microorganisms in ambient water and sediment. However, the extent to which environmental microorganisms can affect shrimp GM composition is unknown. We analyzed the impact of water and sediment microorganisms on the GM of Macrobrachium rosenbergii at different growth stages. We collected water, sediment, and M. rosenbergii gut samples at the early, middle, and late stages of an M. rosenbergii culture and analyzed the microbiota composition. The shrimps’ body weight differed significantly between sampling stages. The shrimp GM composition differed significantly from that of the ambient water and sediment, and these differences were remarkably stronger than those between the shrimp GM at different sampling times and in different ponds. The proportion of sediment bacteria in the shrimp GM was approximately three times higher than that of water bacteria, which changed among ponds and over sampling time. These results provide important reference information for a deeper understanding of the impact of environmental microorganisms on the composition of shrimp GM. Moreover, the results also provide reference information for increasing the production of shrimp culture as well as ensuring a good health status of the culture.

Spatiotemporal Variation of Planktonic Rotifers in Surface Water of a Eutrophic Reservoir in the Southern Subtropical Region of China (2011‒2020) Пространственно-временная изменчивость планктонных коловраток в поверхностных водах эвтрофного водохранилища в южном субтропическом регионе Китая (2011‒2020 гг.)