Eco-efficiency of freshwater aquaculture in China: an assessment considering the undesirable output of pollutant emissions

The eco-efficiency of freshwater aquaculture reflects the balance between freshwater fishery economy and ecological environment. Reasonable evaluation of eco-efficiency is of great significance to improve production value and reduce pollutant emissions. This study analyzes the eco-efficiency of China's freshwater aquaculture from 2004 to 2019, based on SBM model and global Malmquist-Luenberger (GML) index model. Furthermore, it investigates the factors affecting the change of green total factor productivity (GTFP) in freshwater aquaculture according to GML decomposition index. The results show that the eco-efficiency of China's freshwater aquaculture presents an improving trend, but it is still low. From a regional perspective, the eco-efficiency in coastal areas is better than that in non-coastal areas, and both regions are characterized by "high in the north and low in the South." From the perspective of input and output, there is redundancy in factor input. The production value expansion potential shows an inverted "U" shape and gradually tends to saturation. The overall performance of pollutant emissions reduction potential is declining, and there is still potential for improvement. In addition, there is a GTFP change of 0.886-1.262 a year, where the dominating contribution is technology change (TC). According to the research results, the corresponding countermeasures and suggestions are put forward.