Tanglin Zhang

Factors influencing the grass carp gut microbiome and its effect on metabolism

Gut microbiota have attracted extensive attention recently because of their important role in host metabolism, immunity and health maintenance. The present study focused on factors affecting the gut microbiome of grass carp (Ctenopharyngodon idella) and further explored the potential effect of the gut microbiome on metabolism. Totally, 43.39 Gb of screened metagenomic sequences obtained from 24 gut samples were fully analysed. We detected 1228 phylotypes (116 Archaea and 1112 Bacteria), most of which belonged to the phyla Firmicutes, Proteobacteria and Fusobacteria. Totally, 41335 of the detected open reading frames (ORFs) were matched to Kyoto Encyclopedia of Genes and Genomes pathways, and carbohydrate and amino acid metabolism was the main matched pathway deduced from the annotated ORFs. Redundancy analysis based on the phylogenetic composition and gene composition of the gut microbiome indicated that gut fullness and feeding (i.e. ryegrass vs. commercial feed, and pond-cultured vs. wild) were significantly related to the gut microbiome. Moreover, many biosynthesis and metabolism pathways of carbohydrates, amino acids and lipids were significantly enhanced by the gut microbiome in ryegrass-fed grass carp. These findings suggest that the metabolic role played by the gut microbiome in grass carp can be affected by feeding. These findings contribute to the field of fish gut microbial ecology and also provide a basis for follow-up functional studies.

Comparison of intestinal bacterial communities in grass carp, Ctenopharyngodon idellus, from two different habitats

The intestinal bacteria of vertebrates form a close relationship with their host. External and internal conditions of the host, including its habitat, affect the intestinal bacterial community. Similarly, the intestinal bacterial community can, in turn, influence the host, particularly with respect to disease resistance. We compared the intestinal bacterial communities of grass carp that were collected from farm-ponds or a lake. We conducted denaturing gradient gel electrophoresis of amplified 16S rRNA genes, from which 66 different operational taxonomic units were identified. Using both the unweighted pair-group method with arithmetic means clustering and principal component analysis ordination, we found that the intestinal bacterial communities from the two groups of pond fish were clustered together and inset into the clusters of wild fish, except for DF-7, and there was no significant correlation between genetic diversity of grass carp and their intestinal bacterial communities (Mantel one-tailed test, R=0.157, P=0.175). Cetobacterium appeared more frequently in the intestine of grass carp collected from pond. A more thorough understanding of the role played by intestinal microbiota on fish health would be of considerable benefit to the aquaculture industry.

Increased food intake in growth hormone-transgenic common carp (Cyprinus carpio L.) may be mediated by upregulating Agouti-related protein (AgRP).

In fish, food intake and feeding behavior are crucial for survival, competition, growth and reproduction. Growth hormone (GH)-transgenic common carp exhibit an enhanced growth rate, increased food intake and higher feed conversion rate. However, the underlying molecular mechanisms of feeding regulation in GH-transgenic (TG) fish are not clear. In this study, we observed feeding behavior of TG and non-transgenic (NT) common carp, and analyzed the mRNA expression levels of NPY, AgRP I, orexin, POMC, CCK, and CART I in the hypothalamus and telencephalon after behavioral observation. We detected similar gene expression levels in the hypothalamus of TG and NT common carp, which had been cultured in the field at the same age. Furthermore, we tested the effects of GH on hypothalamus fragments in vitro to confirm our findings. We demonstrated that TG common carp displayed increased food intake and reduced food consumption time, which were associated with a marked increase in hypothalamic AgRP I mRNA expression. Our results suggest that elevated GH levels may influence food intake and feeding behavior by upregulating the hypothalamic orexigenic factor AgRP I in GH-transgenic common carp.

Maintaining Economic Value of Ecosystem Services Whilst Reducing Environmental Cost: A Way to Achieve Freshwater Restoration in China

Freshwater fisheries are central to food security in China and this remains one of the most important priorities for the growing human population. Thus, combining ecosystem restoration with economics is pivotal in setting successful conservation in China. Here, we have developed a practical management model that combines fishery improvement with conservation. For six years, a ban on fertilizer and a reduction of planktivorous fish stocking along with the introduction of both mandarin fish Siniperca chuatsi and Chinese mitten crab Eriocheir sinensis was apparent in Wuhu Lake, a highly eutrophic lake located in the middle reaches of the Yangtze River. Annual fish yield decreased slightly after the change in management, whereas fisheries income increased 2.6 times. Mandarin fish and Chinese mitten crab accounted for only 16% of total fisheries production but for 48% of total fisheries income. During this six year period, water clarity increased significantly from 61 cm to 111 cm. Total nitrogen, total phosphorus and chlorophyll decreased significantly from 1.14 to 0.84 mg/L, 0.077 to 0.045 mg/L, and 21.45 to 11.59 μg/L respectively, and macrophyte coverage increased by about 30%. Our results showed that the ecological status of shallow lakes could be rapidly reversed from eutrophic to oligotrophic using simple biomanipulation, whilst maintaining fisheries economic value. It also offers a better approach to shallow fisheries lake management in Asia where traditionally the stocking of Chinese carp and use of fertilizers is still popular.

Effects of Growth Hormone (GH) Transgene and Nutrition on Growth and Bone Development in Common Carp

Limited information is available on effects of growth hormone transgene and nutrition on growth and development of aquatic animals. Here, we present a study to test these effects with growth-enhanced transgenic common carp under two nutritional conditions or feeding rations (i.e., 5% and 10% of fish body weight per day). Compared with the nontransgenic fish, the growth rates of the transgenic fish increased significantly in both feeding rations. The shape of the pharyngeal bone was similar among treatments, but the transgenic fish had relatively smaller and lighter pharyngeal bone compared with the nontransgenic fish. Calcium content of the pharyngeal bone of the transgenic fish was significantly lower than that of the nontransgenic fish. Feeding ration also affected growth rate but less of an effect on bone development. By manipulating intrinsic growth and controlling for both environment (e.g., feeding ration) and genetic background or genotype (e.g., transgenic or not), this study provides empirical evidence that the genotype has a stronger effect than the environment on pharyngeal bone development. The pharyngeal bone strength could be reduced by decreased calcium content and calcification in the transgenic carp.

Co-occurring bighead and silver carps show similar food preference but different isotopic niche overlap in different lakes

Silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) are among the most important fish species in aquaculture and have been introduced to many countries. The feeding ecology of these filter-feeding cyprinids is not well understood and has been mostly based on gut content analyses. We analyzed δ13C and δ15N stable isotope ratios of food resources and fish muscle tissues in four Chinese lakes, where these two species co-occur. Data analysis through Bayesian mixing models revealed that both fish species had similar diets within lakes, and where dietary shifts occurred, both species displayed dietary shifts simultaneously. Diet was generally based on plankton, however, detritus was the main food in eutrophic lake subjected to urban pollution, likely due to resource availability. Niche overlap and width were also variable but in general clear size-based resource partitioning was observed, with bighead carp preying more on zooplankton and occupying a higher trophic position and silver carp feeding more on phytoplankton. Food particles smaller than 64 μm, had little importance in their diets.

Risk-taking behaviour may explain high predation mortality of GH-transgenic common carp Cyprinus carpio.

The competitive ability and habitat selection of juvenile all-fish GH-transgenic common carp Cyprinus carpio and their size-matched non-transgenic conspecifics, in the absence and presence of predation risk, under different food distributions, were compared. Unequal-competitor ideal-free-distribution analysis showed that a larger proportion of transgenic C. carpio fed within the system, although they were not overrepresented at a higher-quantity food source. Moreover, the analysis showed that transgenic C. carpio maintained a faster growth rate, and were more willing to risk exposure to a predator when foraging, thereby supporting the hypothesis that predation selects against maximal growth rates by removing individuals that display increased foraging effort. Without compensatory behaviours that could mitigate the effects of predation risk, the escaped or released transgenic C. carpio with high-gain and high-risk performance would grow well but probably suffer high predation mortality in nature.

Analyzing the importance of top-down and bottom-up controls in food webs of Chinese lakes through structural equation modeling

Zooplankton is generally affected by both top-down and bottom-up regulations in aquatic ecosystems. However, the relative strength of top-down and bottom-up controls on zooplankton assemblages is not well understood. Here, we analyzed this question in five lakes of the Yangtze River basin, an area with high population density and thousands of lakes, many of them suffering multiple environmental pressures. We sampled the whole communities of five lakes in the middle reaches of Yangtze River basin from 2006 to 2011 and used structural equation modeling to evaluate the relative importance of joint top-down and bottom-up effects. With increasing total phosphorous (TP), a major shift occurred in trophic structure. Biomass of phytoplankton, rotifers, cyclopoids, and planktivorous fish significantly increased, while cladocerans and calanoids were negatively correlated with increasing TP. The bottom-up effects were strongest at the bottom of the food web (e.g., effects of TP on phytoplankton). Direct bottom-up effects of phytoplankton and other food resources (latent variable) on rotifers and cyclopoids were greater than top-down controls from planktivores. The predation pressure on crustacean zooplankton by planktivores was higher than that on rotifers. In planktivore-dominated systems, piscivores only played a marginal role, whereas they seem affected by water quality. These results suggest not only in the food web processes the important role of nutrient pollution in affecting the top of the food web in these lakes, but also that the impacts and relative strength of bottom-up and top-down controls may vary with zooplankton assemblages, indicating the complexity of food webs in degraded lakes in China.

Assessing fish distribution and threats to fish biodiversity in the Yangtze River Basin, China

The Yangtze River (6,380 km long) is the longest river inAsia and the third-longest one in the world. Its river basin(a complex riverine–lacustrine network) is especially richin fish fauna, representing high species richness andendemism, and therefore is a globally significant area forpreserving fish biodiversity (Dudgeon 2000; Park et al.2003). However, during the past several decades, loss offish biodiversity in the Yangtze River Basin has beenaccelerated by a series of direct and indirect effects ofhuman activities and environmental changes, e.g., disap-pearance, shrinkage, and fragmentation of habitats for fishspawning, feeding and migration, overfishing, water pol-lution, and invasion of exotic species (Zeng 1990; Xie andChen 1999). Despite numerous publications on ichthyo-logical research in the Yangtze River Basin since the1950s, synthesis and analysis or assessment of fish distri-bution patterns and quantification of major threats to fishesare still limited, which in turn limits formulation of bio-diversity conservation strategies. In this study, we collectedand synthesized the scattered data from relevant literature,with the purposes of (1) assessing large-scale distributionand endemic species composition of Yangtze fishes, (2)ranking the contribution of major threats as well as intrinsicfactors to fish endangerment, and (3) providing recom-mendations for fish conservation in the basin.The Yangtze River Basin consists of five defined areas(Fig. 1). The riverhead is located on the Tibetan Plateau,where the mean elevation is over 4,500 m (Zeng 1990).The upper reach extends upstream from Yichang (in HubeiProvince), with a length of more than 4,300 km and adrainage basin area of 100 9 10

Effects of turbidity and light intensity on foraging success of juvenile mandarin fish Siniperca chuatsi (Basilewsky)

This study aimed to evaluate the effects of turbidity and light intensity on foraging success of juvenile mandarin fish Siniperca chuatsi. Predation on crucian carp Carassius auratus by juvenile mandarin fish was tested at five levels of turbidity combined with two light intensities, imitating daylight and night in two turbidity types. Foraging success was significantly lower in clay-induced turbidity than in algal-induced turbidity. In clay-induced turbidity trials, there was a slight but insignificant increase in foraging success of mandarin fish with increasing turbidity under lighted conditions. In algal-induced turbidity trials, there were no significant differences in foraging success of mandarin fish among turbidity levels at both light and dark levels, but at 80 NTU turbidity level, foraging success was lower than in all the other turbidity levels. There was no significant difference in foraging success at different turbidities under darkness. These results suggest that piscivory of mandarin fish is influenced by different turbidity types but is not significantly influenced by increased turbidity combined with decreased light intensity.