Dissolved oxygen and ammonia affect ammonia production via GDH/AMPK signaling pathway and alter flesh quality in Chinese perch (Siniperca chuatsi).

The dissolved oxygen (DO) and ammonia are crucial to the growth of Chinese perch (Siniperca chuatsi). Information on the effects of DO and total ammonia nitrogen (TAN) in regulating ammonia nitrogen excretion and flesh quality in Chinese perch is scanty. This study aimed to evaluate the effects of dissolved DO at oxygen levels of 3 mg/L and 9 mg/L, as well as the TAN concentrations of 0.3 mg/L and 0.9 mg/L on ammonia excretion and flesh quality. Results showed that the ammonia contents in plasma, muscle, and liver of the 9 mg/L DO group were significantly higher than those of the 3 mg/L DO group (P < 0.05). However, the expression of AMPK-related signaling pathway genes (gdh, lkb1, and ampd) and flesh quality indicators (gumminess, chewiness, hardness) in the 9 mg/L DO group were significantly lower than those in the 3 mg/L DO group. Under long-term exposure to 0.9 mg/L TAN, the ammonia contents in plasma and gill filaments, as well as muscle flesh quality (resilience, gumminess, chewiness, cohesiveness), were significantly lower than those in the 0.3 mg/L TAN group (P < 0.05). However, the activities of GDH and AMPD enzymes in the 0.9 mg/L TAN group were significantly higher than those in the 0.3 mg/L TAN group. In summary, when fish are exposed to 3 mg/L DO and 0.9 mg/L TAN in the environment for a long time, their amino acids are used for transamination and deamination, resulting in insufficient energy supply for Chinese perch, whereas 9 mg/L DO and 0.9 mg/L TAN caused deterioration of the flesh quality.

Occurrence and translocation of ustiloxins in rice false smut-occurred paddy fields, Hubei, China.

Ustiloxin A (UA) and ustiloxin B (UB), two major mycotoxins produced by the pathogen of rice false smut (RFS) during rice cultivation, have attracted increasing attentions due to their potential health risks. However, limited data are available about their occurrence and fate in paddy fields and contamination profiles in rice. In this study, a field study was performed to investigate the occurrence and translocation of UA and UB in RFS-occurred paddies. For the first time to our knowledge, we reported a ubiquitous occurrence of the two ustiloxins in the paddy water (range: 0.01-3.46 µg/L for UA and <0.02-1.15 µg/L for UB) and brown rice (range: 0.09-154.08 µg/kg for UA and <0.09-23.57 µg/kg for UB). A significant positive correlation was observed between ustiloxin levels in paddy water and brown rice (rs = 0.48-0.79, p < 0.01). The occurrence of ustiloxin uptake in water-rice system was also evidenced by the rice exposure experiment, suggesting paddy water might be an important source for ustiloxin accumulation in rice. These results suggested that the contamination of ustiloxins in rice might occur widely, which was supported by the significantly high detection frequencies of UA (96.6%) and UB (62.4%) in polished rice (149 samples) from Hubei Province, China. The total concentrations of ustiloxins in the polished rice samples collected from Hubei Province ranged from <20.7 ng/kg (LOD) to 55.1 µg/kg (dry weight). Further studies are needed to evaluate the potential risks of ustiloxin exposure in the environment and humans.