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The gut microbiota of aquatic animals plays a crucial role in host health through nutrient acquisition and outcompetition of pathogens. In this study, on the basis of the highthroughput sequencing of 16S rRNA gene amplicons, we examined the bacterial communities in the gut of freshwater shrimp (Macrobrachium nipponense) and in their living environments (sediment and pond water) and analyzed the effects of abiotic and biotic factors on the shrimp gut bacterial communities. High bacterial heterogeneity was observed in the freshwater shrimp gut samples, and the result indicated that both the surrounding bacterial community and water quality factors (particularly dissolved oxygen and temperature) could affect the shrimp gut bacterial community. Despite the observed heterogeneity, 57 genera, constituting 38-99% of the total genera in each of the 40 shrimp gut samples, were identified as the main bacterial population in the gut of M. nipponense. In addition, a high diversity and abundance of lactic acid bacteria (26 genera), which could play significant roles in the digestion process in shrimp, were observed in the shrimp gut samples. Overall, this study provides insights into the gut bacterial communities of freshwater shrimp and basic information for shrimp farming regarding the application of probiotics and disease prevention.

Nitrous oxide (N 2 O) emission of fresh invertebrates has too long been neglected in eutrophic lakes

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at six sampling sites in Lake Taihu in order to determine the spatial and temporal variation in fish assemblages in Lake Taihu and to assess the influence on fish assemblages of eutrophication and disconnection of migration routes. A total of 134,604 specimens (1456.7 kg total biomass) were caught, representing 61 species, 18 families, and 10 orders. Cyprinidae fish (36 species) contributed most of the total species richness and the most dominant species was Coilia nasus. Sampling months and sampling sites each significantly affected the Margalef richness index, ShannonÀWiener diversity index (H 0 ), and Pi elou's evenness index (J 0 ) of fish assemblages and there were interactive effects between them. The ANOSIM analysis indicated that the fish assemblage structure had significant differences among the sample sites. Total nitrogen (TN) and total phosphorus (TP) both differed significantly among sites. The results of correlation analyses suggested that there was a significant negative correlation between two indices (H 0 and J 0 ) and both TP and TN (p < 0.01) as well as a significant positive correlation of catch per unit effort with both TP and TN (p < 0.01). Our results suggest that eutrophication in Lake Taihu has led to an increase in small-sized phytoplanktivorous and zooplanktivorous fishes and a decrease in prey availability for predatory fishes. Thus, the relative importance of small-sized fishes has increased and a few small-sized species (e.g., C. nasus) have become the dominant species, as reflected by reductions in the species diversity indices (H 0 and J 0 ).Keywords: species composition; species diversity; fish assemblage; Lake Taihu; fish community IntroductionFloodplains lakes are dynamic systems that are used by many freshwater fish as nursery sites, migration routes, feeding, and breeding areas. Many researchers have shown that fish assemblages in lakes exhibit spatial and/or temporal variation because of environmental fluctuations and anthropogenic activities (Gaudrear & Boisclair 1998; TejerinaGarro et al. 1998;Jackson et al. 2001;Ru et al. 2008;Menezes et al. 2013;Ru & Liu 2013). Lakes are closely linked to human activity and have been altered as a result of urban and industrial development throughout the world (Scheffer et al. 2001;Qin et al. 2006). Fish assemblage structure and diversity also are changed and threatened because *Corresponding author. Email: tskwell@163.comJournal of Freshwater Ecology, 2015 Vol. 30, No. 1, 181À196, http://dx.doi.org/10.1080/02705060.2015 of eutrophication, riverÀlake isolation, and over-fishing (Vonlanthen et al. 2012;Ru & Liu 2013). Thus, the importance of the fish community as a biological indicator of human-induced changes in lake ecosystems is reinforced and to conserve fish, appropriate management actions are made possible by surveys of relevant fish communities (Jones & West 2005;Menezes et al. 2013;Ru & Liu 2013). Lake Taihu is located in the Yangtze Delta plain, one of the largest floodplains in the world, with numerous shallow lakes distributed ...