Non-fed aquaculture is an important contributor to low environmental impact protein production. However, knowledge of spatiotemporal patterns of the fish community in non-fed fishery systems remains limited, despite their ecological importance for sustainable aquaculture and fisheries. To elucidate the status of the fisheries and their critical drivers in non-fed fishery systems, hydroacoustic surveys were conducted seasonally in Hongchaojiang Reservoir in two seasons (spring and autumn) of two consecutive years: 2018 and 2019. Results showed that the average fish density in Hongchaojiang Reservoir was 121.6 ind./1000 m³. Fish communities varied significantly between geographical locations and seasons. On the temporal scale, fish densities in October were higher than those in April. On the spatial scale, fish densities were higher in the upstream (S1 and S3) than those in the midstream (S2, S4, S5, S6), while the density of S7, S8 and S9 in the downstream was the lowest. Trophic level index, zooplankton, chlorophyll-a, and phytoplankton play vital roles in fish distributional patterns, while the target strength, which reflects fish body size, was highly associated with water temperature, dissolved oxygen, total organic carbon, and phytoplankton. These results suggest that the spatiotemporal distribution of the fish community in Hongchaojiang Reservoir was jointly influenced by biotic and abiotic variables of water bodies, and highlight the importance of water nutrient levels and food availability in shaping fish distribution in the non-fed aquaculture system. This study should improve our understanding of ecological patterns and dominant drivers in fish stocks and provide information for successful sustainable management in non-fed purification fisheries.

Introduction: Frequent disease outbreaks seriously affect porcupinefish (Diodon hystrix), which is a new aquaculture breed in China. Recently, a novel disease, termed tail fell syndrome (TFS) was increasingly observed in fish stocks, resulting in stalk ulceration, tail loss, ascites and white feces in the intestine. Intestinal microbiota homeostasis is crucial to host health because it influences host and environmental factors, and responds to various internal and external stimuli. However, changes in intestinal microbiota induced by TFS are yet to be elucidated.Methods: In the present study, we analyzed and compared the intestinal microbiota of normal D. hystrix with TFS fish.Results: Though microbiota richness and diversity were not affected by TFS, deviations in diversity indices increased and taxa distribution evenness decreased, suggesting TFS lowered microbiota community stability in D. hystrix. Furthermore, at the genus level, Brevibacterium, Mesorhizobium, Ochrobactrum, Ralstonia, Anaerococcus, and Alistipes abundances were significantly increased in TFS D. hystrix, plus, we observed significant decreases in Halomonas, Prevotellaceae_NK3B31_group, and Psychrobacter. Functional comparison predictions between normal and TFS D. hystrix revealed significantly altered pathways were mainly associated with metabolism (biotin metabolism, steroid hormone biosynthesis, flavonoid biosynthesis, biosynthesis of type II polyketide products, and steroid biosynthesis). Overall, the results revealed that TFS impacted intestinal microbiota composition and function in D. hystrix, which should expand our knowledge on diseases associated with porcupine pufferfish aquaculture.