Qingfei Zeng

Molecular characterization and expression analysis of five chitinases associated with molting in the Chinese mitten crab, Eriocheir sinensis.

Chitinases are crucial enzymes required for chitin degradation in crustaceans. Five chitinase genes, namely, EsCht1, EsCht2, EsCht3, EsCht4, and EsCht6, were identified in the Chinese mitten crab, Eriocheir sinensis. The open reading frames (ORF) of EsCht1, EsCht2, EsCht3, EsCht4 and EsCht6 ranged from 1182 bp to 1926 bp with encoding proteins between 393 and 641 amino acid residues. Domain analysis of the chitinase proteins showed that most EsChts contained the catalytic domain and the chitin-binding domain (CBD) connected with the serine/threonine (S/T)-rich linker region. Phylogenetic analyses revealed that EsChts with orthologs in crustaceans were divided into six groups. The tissue-dependent, developmental stage-related and molting stage-related differential expression patterns of chitinase genes were determined using end-point polymerase chain reaction and real-time quantitative polymerase chain reaction. During the molting cycle, EsCht2 mRNA expression in the cuticle and EsCht4 and EsCht6 mRNA expression in the hepatopancreas were 108-fold (P<0.05), 19-fold (P<0.05) and 12-fold (P<0.05) higher in the premolt (D(0-1)) than in the intermolt stage, respectively. The results indicated that EsCht1 from group 1 might play a role in the digestion of chitin-containing food; EsCht2 from group 2 likely played a role in the degradation of chitinous cuticle during molting for growth and during the post-embryonic development; EsCh3 from group 3 potentially had a dual role in the digestion of chitin-containing food and defense against chitin-bearing pathogens. EsCht3, EsCht4, and EsCht6 were highly expressed in the reproductive system, indicating their potential roles in reproductive molting. Differential expression patterns of the chitinase genes suggested that they might have distinct biological functions in developmental stage- and physiological growth-related and reproductive molting processes, which are essential for metamorphosis, growth, and reproduction. The findings of this study might form a basis for further studies on the functions of chitinases in E. sinensis and other crustaceans.

Food web structure of a shallow eutrophic lake (Lake Taihu, China) assessed by stable isotope analysis

Lake Taihu is a large, shallow, and eutrophic lake in China. It has provided local communities with valuable fisheries for centuries, but little is known of the trophodynamics, or of its faunal communities. Carbon and nitrogen isotopic composition was used to assess its trophic pathways and the food web structure [food sources and trophic levels (TL)]. Basal food sources were distinguishable based on their δ13C values, ranging from −27.2 to −15.2‰. Consumers were also well separated in δ13C (−26.9 to −17.9‰ for invertebrates and −25.7 to −18.1‰ for fishes), which allowed for an effective discrimination of carbon sources between these fauna. An average trophic enrichment factor of 3.4‰ was used to calculate the TLs based on δ15N of zooplankton, with results indicating a food web having four TLs. Although δ15N values overlap and cover a large range within trophic compartments, the isotopic signatures of the species assessed revealed a general trend of 15N enrichment with increasing TL. Stable isotope signatures were also used to establish a general food web scheme in which five main trophic pathways were analyzed.

Seasonal and spatial variations of the food web structure in a shallow eutrophic lake assessed by stable isotope analysis

Stable isotope analysis was used to investigate seasonal and spatial variations of the food web structure in a large eutrophic lake ecosystem (Lake Taihu, China). Basal food sources, invertebrates and fish were sampled in two lake regions with different environmental conditions and spatial variations in the isotopic composition of lake food webs were found. Overall, more depleted δ13C and enriched δ15N isotope values of organic matter sources and consumers were found in the phytoplankton-dominated lake region than in the macrophyte-dominated region. Wide seasonal variations in the isotopic ratios were also observed in the lake biota, with a general trend towards enriched δ13C and δ15N values in summer and depleted values in winter. This pattern could be explained by a combination of environmental (e.g., irradiance and nutrient inputs) and biotic (e.g., availability of food sources and plasticity in prey item choice) features. Results of isotope mass balance suggest that macrophytes provide some trophic support in the macrophyte-dominated area, but in both lake regions it is more likely that aquatic food webs are phytoplankton based rather than macrophyte based under eutrophic conditions.

Distribution, fate and risk assessment of PAHs in water and sediments from an aquaculture- and shipping-impacted subtropical lake, China

The spatial-temporal distribution of polycyclic aromatic hydrocarbons (PAHs), their source, and potential health risks were determined in overlying water and surface sediments from Chinese Lake Guchenghu, adjacent commercial mitten crab ponds and the connected Wushen Canal to assess the contamination profile of the area. The total PAHs concentrations in sediment and water were 86.7-1790 ng g-1 dry weight (dw) and 184-365 ng L-1 in summer and 184-3140 ng g-1 dw and 410-1160 ng L-1 in winter. Two- and 3-ring PAHs were the predominant compounds in water, while PAHs with 4-6 rings dominated in the sediment at both upstream and downstream sites. PAHs concentrations in water and sediment correlated significantly. Diagnostic ratios and positive matrix factorization (PMF) analyses indicated a strong influence of pyrogenic sources, principally biomass combustion and vehicle emission, on the concentrations of PAHs. The distribution, source identification, and mean effects range median quotients (mERMQ) analyses suggested that the most contaminated area was located downstream and upstream of the Wushen Canal, followed by Lake Guchenghu and a commercial crab pond area. From an ecological point of view, PAHs posed a potential risk to drinking water sources as the concentrations exceeded the guideline value of 0.05 μg L-1. The risk posed by sediment PAHs appeared to be low except for the downstream sites, which showed a low to medium ecotoxicological risk. The total incremental lifetime cancer risks ranged between 10-7 and 10-5, indicating a potential health risk for the local population when exposed to sediment from the area.

Dynamics of photosynthetic activity of cyanobacteria after gut passage through crucian carp ( Carassius auratus gibelio ) and goldfish ( Carassius auratus auratus )

The photosynthetic activity of cyanobacteria (predominantly Microcystis spp.) after passage through crucian fish and goldfish was determined by photo-PAM (pulse-amplitude-modulated) during a 17-day cultivation of fish faeces in filtered lake water. The Microcystis exhibited a significant reduction of activity after passage through both crucian carp and goldfish, whereas there was a significant stimulation of photosynthetic activity of diatom and green algae following the depressed cyanobacteria during cultivation. The mainly stimulated eukaryotic algae species were Fragilariaceae and Scenedesmus obliquus by microscopy. Our results provide experimental evidence that Microcystis is damaged by crucian carp and goldfish digestion. That may be useful as a complementary method for combating cyanobacterial blooms and utilizing them for crucian carp and goldfish nutrition.

Antibiotics in Crab Ponds of Lake Guchenghu Basin, China: Occurrence, Temporal Variations, and Ecological Risks

Antibiotics are widely used in aquaculture, however, this often results in undesirable ecological effects. To evaluate the occurrence, temporal variations, and ecological risk of antibiotics in five crab ponds of Lake Guchenghu Basin, China, 44 antibiotics from nine classes were analyzed by rapid resolution liquid chromatography-tandem mass spectrometry (RRLC-MS/MS). Twelve antibiotics belonging to six classes were detected in the aqueous phase of five crab ponds, among which sulfonamides and macrolides were the predominant classes, and six compounds (sulfamonomethoxine, sulfadiazine, trimethoprim, erythromycin-H2O, monensin, and florfenicol) were frequently detected at high concentrations. In general, the antibiotic levels varied between different crab ponds, with the average concentrations ranging from 122 to 1440 ng/L. The antibiotic concentrations in crab ponds exhibited obvious seasonal variations, with the highest concentration and detection frequency detected in summer. Multivariate analysis showed that antibiotic concentrations were significantly correlated with environmental variables, such as total organic carbon, phosphate, ammonia nitrogen, and pH. Sulfadiazine, clarithromycin, erythromycin-H2O, and ciprofloxacin posed a high risk to algae, while the mixture of antibiotics could pose a high risk to aquatic organisms in the crab ponds. Overall, the usage of antibiotics in farming ponds should be comprehensively investigated and controlled to preserve a healthy aquaculture ecosystem.