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The role of glutathione (GSH) and cysteine (Cys) conjugates in the detoxification of microcystin-LR (MC-LR) in bighead carp (Aristichthys nobilis) was examined under laboratory and field conditions. Wild individuals of bighead carp were collected from 5 eutrophic lakes along the Yangtze River, while in laboratory experiment, bighead carp were injected intraperitoneally with 500 lg purified MC-LR/kg body weight (bw). Contents of MC-LR and its glutathione (MC-LR-GSH) and cysteine conjugates (MC-LR-Cys) in the liver of bighead carp were determined by liquid chromatography electrospray ionization mass spectrum (LC-ESI-MS). In laboratory experiment, low concentrations of MC-LR-GSH (mean: 0.042 lg/g dry weight (DW)) were always detectable, and the mean ratio of MC-LR-Cys to MC-LR-GSH was 6.55. While, in field study, relatively high MC-LR-Cys concentration (mean: 0.22 lg/g DW) was detected, whereas MC-LR-GSH was occasionally detectable, and the average ratio of MC-LR-Cys to MC-LR-GSH was as high as 71.49. A positive correlation was found between MC-LR-Cys concentration in the liver of bighead carp and MC-LR content in seston from the five lakes (r = 0.85). These results suggest that MC-LR-Cys might be much more important than MC-LR-GSH in the detoxification of MC-LR in fish liver, and that cysteine conjugation of MC-LR might be a physiological mechanism for the phytoplanktivorous bighead carp to counteract toxic cyanobacteria.

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Many physical, chemical, and biological processes in lakes depend on lake water temperature. However, attribution of the warming rate in a shallow lake is not well understood yet. Here, we evaluated a one-dimensional lake model FLake by observed daily lake surface water temperature (LSWT) at four typical lakes in the Middle and Lower Yangtze River basin and then attributed LSWT warming to climate variables during the period 1979–2017. We found that FLake could capture well the seasonal/interannual variation of observed LSWT. During the 39-year study period, LSWT significantly warms at a rate of 0.26–0.28 °C per decade, 24–35% slower than the air temperature. Increased solar radiation and air temperature contributed to most (>80%) of the LSWT warming. The warming trend of LSWT in the spring is the largest among the four seasons, 2–4 times the warming rate of the other seasons. Brightening in the spring contributes 50–64% of the largest spring warming. The future air warming plus the brightening trend with the Clean Air Act in China would amplify LSWT warming and, thus, advance and/or deteriorate algae blooms, especially in spring.