Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) from a large shallow, eutrophic lake of the subtropical China

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) were studied monthly in a large shallow, eutrophic lake of the subtropical China during June-November, 2003. Microcystins (MCs) were quantitatively determined by High-Performance Liquid Chromatography (HPLC) with a qualitative analysis by a Finnigan LC-MS system. On the average of the study period, hepatopancreas was the highest in MC contents (mean 4.14 and range 1.06-7.42 mug g(-1) DW), followed by digestive tracts (mean 1.69 and range 0.8-4.54 mug g(-1) DW) and gonad (mean 0.715 and range 0-2.62 mug g(-1) DW), whereas foot was the least (mean 0.01 and range 0-0.06 mug g(-1) DW). There was a positive correlation in MC contents between digestive tracts and hepatopancreas. A constantly higher MC content in hepatopancreas than in digestive tracts indicates a substantial bioaccumulation of MCs in the hepatopancreas of the snail. The average ratio of MC-LR/MC-RR showed a steady increase from digestive tracts (0.44) to hepatopancreas (0.63) and to gonad (0.96), suggesting that MC-LR was more resistant to degradation in the snail. Since most MCs were present in the hepatopancreas, digestive tracts and gonad with only a very small amount in the edible foot, the risk to human health may not be significant if these toxic parts are removed prior to snail consumption. However, the possible transference of toxins along food chains should not be a negligible concern. (C) 2004 Elsevier Ltd. All rights reserved.

Seasonal occurrence of Dollfustrema vaneyi (Digenea : Bucephalidae) metacercariae in the bullhead catfish Pseudobagrus fulvidraco in a reservoir in China

The seasonal population dynamics of metacercariae of the bucephalid Dollfustrema vaneyi (Tseng, 1930) Echmann, 1934 in the bullhead catfish Pseudobagrus fulvidraco (Richardson) were investigated in Jiangkou reservoir, Jiangxi Province, east China, during the period from April 1990 to August 1991. In total, 523 fish were obtained, and the overall prevalence of the metacercariae was 89.87 % and mean abundance 136.25 +/- 308.09 (mean +/- SD). A pattern of seasonal changes in prevalence and mean abundance was observed, with higher levels of metacercariae infection in late spring and summer. An analysis of the distribution of D. vaneyi in different organs of P. fulvidraco suggested that the eyes might be a suitable location for the parasite. Furthermore, the possible role of metacercariae in bullhead catfish was discussed in relation to the life cycle of this parasite.

Seasonal patterns in feeding ecology of three small fishes in the Biandantang Lake, China

Feeding ecology of three small fish species, Hypseleotris swinhonis, Ctenogobius giurinus and Pseudorasbora parva was studied seasonally in the Biandantang Lake, a small, shallow lake in central China. Gut length, adjusted for total body length, was significantly higher in spring than in other seasons for all the three species. Seasonal changes in gut length were not associated with changes in food quality. Weight of fore-gut contents, adjusted for body weight, was significantly higher in winter and spring than in summer and autumn in H. swinhonis and C. giurinus, and significantly higher in autumn than in spring and summer for P. parva. Percentage of empty fore-guts was highest in summer and lowest in spring for I-I. swinhonis and C. giurinus, and highest in winter and lowest in autumn for P. parva. Diet of the three small fishes showed apparent seasonal changes, and these changes reflected partly the seasonal fluctuations of food resources in environment. Diet breadth was high in winter and low in autumn for H. swinhonis, high in winter and low in spring and summer for C. giurinus, and high in autumn and low in spring for P. parva. Diet overlaps between pairs of species were biologically significant in most cases, except between H. swinhonis and P. parva in summer and autumn and between C. giurinus and P. parva in autumn. (C) 2000 The Fisheries Society of the British Isles.

Seasonal population dynamics of parasitic copepods, Sinergasilus spp. on farmed fish in China

Seasonal population dynamics of parasitic copepods in the genus Sinergasilus on fanned silver carp Hypophthalmichthys molitrix, farmed bighead carp Aristichthys nobilis, and grass carp Ctenopharyngodon idellus were investigated in China. Changes in prevalence and abundance were seasonal with higher levels observed in summer. Reproduction of the copepods occurs from spring to early autumn as indicated by the higher ratio of gravid copepods. The frequency distribution of Sinergasilus polycolpus and S. major in their host populations can be fitted well with negative binomial distribution. (C) 2000 Elsevier Science B.V. All rights reserved.

Seasonal variation in kinetic parameters of alkaline phosphatase activity in a shallow Chinese freshwater lake (Donghu Lake)

Seasonal variation of the kinetic parameters of total alkaline phosphatase activity (APA) was studied in a shallow Chinese freshwater lake (Donghu Lake). At the three experimental stations the values of V-max of APA were higher and the negative correlation between orthophosphate and the total APA specific activity (V-max/Chl.) was stronger during summer (from June to September) P depletion. At the same time, the values of Michaelis constant (K-m) of APA at the three stations decreased. Phytoplankton seem to compensate for their phosphorus deficiency not only by an increase in enzyme production but also by an improved ability to use low substrate concentrations. (C) 1997 Elsevier Science Ltd.

UV-sensitive P compounds: Release mechanism, seasonal fluctuation and inhibitory effects on alkaline phosphatase activity in a shallow Chinese freshwater lake (Donghu Lake)

Filtrable phosphorus compounds in a shallow Chinese freshwater lake (Donghu Lake) were fractionated by Sephadex G-25 gel-filtration chromatography. Some portions of those compounds released soluble reactive phosphorus upon irradiation with low dose ultraviolet light. Catalase and a hydroxyl radical scavenger (mannitol) markedly prevented photosensitive phosphorus release. The observed effects may be explained by the action of oxidizing reagents such as hydroxyl radicals, produced in photochemical reactions between UV irradiation and humic substances in the water. There was a strong seasonality in UV-sensitive P (UVSP) release. Michaels constants (K-m) of total alkaline phosphatase in the lake water showed a direct positive relation to UVSP. Plot of K-m against the UVSP/phosphomonoester ratio reveals a strong relationship between the two variables. These results suggest that in some situations UVSP may be a competitive inhibitor of alkaline phosphatase activity in the lake. The competitive inhibition of fractionated UVSP on alkaline phosphatase reagent (Sigma) apparently supports this hypothesis.

Spatial and seasonal distributions of carbonaceous aerosols over China

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Seasonal migration of cirrus clouds over the Asian Monsoon regions and the Tibetan Plateau measured from MODIS/Terra

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