养殖密度对花鲈肠道、养殖池塘水体和沉积物菌群结构的影响OA

Intensive pond-based aquaculture of marine fish can generate substantial economic benefits.However,increased feed inputs and the accumulation of residual feed and excretion lead to elevated organic matter levels,which deteriorate water quality and subsequently alters the microbial community structure of the pond ecosystem.Similarly,microbial communities participate in water quality regulation and nutrient cycling through their growth,metabolism,and reproduction.Therefore,understanding the dynamic characteristics of pond microbiota can help improve the aquaculture water environment through microecological regulation,thereby providing a theoretical foundation for optimizing intensive and sustainable aquaculture practices. Spotted sea bass(Lateolabrax maculatus)is one of the important economically important aquaculture species in China,with Guangdong Province accounting for 71.18%of national production.Intensive pond-based culture represents the dominant farming mode for L.maculatus in Guangdong Province.However,there are currently no published studies on the microecological structure of the gut,pond water,and sediment of L.maculatus,nor on their responses to stocking density regulation.In this study,two experimental ponds,each with an area of approximately 6203 m2,were randomly selected.Two contrasting stocking densities were established:high density(87.7 inds/m3)and low density(41.4 inds/m3).Samples of pond water,sediment,and juvenile gut were collected during both moderate-temperature and high-temperature periods.Using 16S rRNA high-throughput sequencing,the microbial community structure of different pond components was systematically investigated.The results showed that sediment microbiota exhibited the highest α-diversity among all sampled components.During the high-temperature period,sediment α-diversity in the high-density group was significantly higher than that observed in the low-density group.However,water α-diversity exhibited the opposite trend during the moderate-temperature period.Specifically,during the moderate-temperature period,water α-diversity was significantly higher in the low-density group.Higher stocking density altered the α-diversity index of juvenile gut microbiota,although the difference was not statistically significant.Proteobacteria,Bacteroidota,Firmicutes,and Actinobacteriota were identified as the dominant phyla in pond water,sediment,and juvenile gut samples.Stocking density significantly altered the relative abundances of Proteobacteria,Actinobacteriota,Bacteroidota,Gemmatimonadota,Acidobacteriota,Desulfobacterota,and Nitrospirota in both sediment and water(P<0.05).These dominant phyla play key roles in carbon,nitrogen,and phosphorus cycling and utilization.These findings indicate that density-induced changes in the aquaculture water quality further regulate microbial community dynamics,thereby maintaining functional stability and supporting water quality regulation.A higher stocking density reduced the Firmicutes to Bacteroidota ratio in the juvenile gut,suggesting lower energy accumulation efficiency in the high-density group,which may be related to increased energy consumption due to density stress.Amplicon sequence variant(ASV)analysis indicated that,compared with sediment,water microbiota had a greater influence on the gut microbiota of L.maculatus.Moreover,water microbiota resulted from the combined influences of gut and sediment microbiota,reflecting the complexity of the microecological structure in the pond system.This finding also explains why the number of ASVs in water was intermediate between that in sediment and gut.KEGG pathway analysis revealed that,during the moderate-temperature period,the abundance of microbial genes enriched in nutrient-metabolism pathways in the high-density water group was significantly lower than that in the low-density group(P<0.05).This suggests a decline in microbial functional capacity related to nutrient absorption and metabolism,which may impair growth and reproduction and could explain the lower α-diversity and total ASVs in the high-density group.Together with changes in dominant phyla,this may be associated with a significant reduction in the relative abundance of Bacteroidota,Firmicutes,and Gemmatimonadota in the high-density group.During both moderate-and high-temperature periods,the abundances of microbial genes enriched in cellular community-prokaryote and signal transduction pathways were significantly higher in the high-density sediment group than that in the low-density group(P<0.05).This pattern reflects greater environmental stress in high-density pond habitats,where microbiota in sediment primarily exhibit functions associated with environmental adaptation. In conclusion,higher stocking density of L.maculatus significantly altered microbial α-diversity in water during the moderate-temperature period and in sediment during the high-temperature period.Proteobacteria,Bacteroidota,Firmicutes,and Actinobacteriota were identified as the dominant phyla across water,sediment,and gut habitats.Stocking density notably influenced the relative abundance of major phyla in water(e.g.,Proteobacteria,Firmicutes,Bacteroidota,Acidobacteriota,and Gemmatimonadota)and sediment(e.g.,Bacteroidota,Actinobacteriota,and Gemmatimonadota).Microbial communities adapted to their environments by adjusting functional profiles to nutrient metabolism,energy acquisition,and environmental sensing.However,stocking density did not significantly alter the overall gut microbiota structure of L.maculatus.As an ecological medium,water played a critical role in shaping the microbiota of both the gut and sediment.