Assessment of antibacterial properties and the active ingredient of plant extracts and its effect on the performance of crucian carp (Carassius auratus gibelio var. E'erqisi, Bloch).

BACKGROUND: In this study, the antibacterial properties and active ingredient of plant extracts and its effect on the performance of crucian carp (Carassius auratus gibelio var. E'erqisi, Bloch) were assessed. RESULTS: The transmission electron microscopy and flow cytometric analysis showed that the antibacterial activity of plant extracts is due to the disruption of the cell membrane and the leakage of cytoplasmic contents. The UPLC-MS/MS analysis showed that the contents of gallic acid, (-)-epigallocatechin, (+)-catechin, (-)-epigallocatechin gallate, (-)-epicatechin gallate, aloe-emodin, rhein, emodin, chrysophanol, and physcion, were 5.27%, 3.30%, 1.08%, 19.32%, 5.46%, 0.23%, 0.56%, 1.28%, 0.75% and 0.39% in plant extracts, respectively. Results of feeding experiment showed that feeding crucian carp with 1.0% and 2.0% plant extracts significantly enhanced specific growth rate, serum total protein, lysozyme, catalase and superoxide dismutase activities, and decreased the feed conversion rate, malondialdehyde contents and the mortality rate (P < 0.05). CONCLUSION: It can be concluded that plant extracts added to fish feed can act as natural antimicrobial and immunostimulants to prevent pathogenic infection, enhance immune response, and promote growth of the fish.

[Economic values of nitrogen transformation in rice field ecosystems].

Based on the 2002 field experimental results in the Wusi Farm of Fengxian County in Shanghai and related studies, and by the methods of ecological economy and environmental economy, this article examined and estimated the nitrogen input and output, and the economic values of nitrogen transformation in rice field ecosystems. The results indicated that the plot without N fertilization showed a deficit of nitrogen budget, while those with urea application showed a surplus. The economic value of the plot without urea amendment was evaluated to be positive, while that of the plots with urea application was calculated to be negative. The negative value of the plots with urea amendment resulted from the nitrogen losses through ammonia volatilization, nitrogen leaching and runoff, which had serious harmful impacts on environment and human society. Therefore, only when some measures were taken to encourage and facilitate farmers to improve the efficiency of urea application and to mitigate the environment problems from N losses in the process of food production, the advantages of nitrogen transformation in rice fields could be promoted, and the sustainability of agriculture would become reality.