Comparative study on the carbon footprints of extruded and pelleted feed and their potential for carbon reduction: A case study of grass carp feed

China is the largest aquaculture producer, and grass carp ranks first in the freshwater fish industry. Fish feed is considered among the most important contributor to the impacts of the aquaculture industry. This study aimed at analyzing the different global warming potentials (i.e., carbon footprint; CF) of extruded and pelleted grass carp feed by implementing the life cycle assessment (LCA) method. The cradle-to-gate system boundaries of aqua -culture feed includes the raw material production phase, transportation phase, and processing phase, and data were obtained from field investigation, the Ecoinvent 3.7.1 database, and academic references. Furthermore, the CF and emission reduction potential of the entire freshwater fish feed industry in China was estimated, thus providing a basis for decision-makers to achieve carbon neutrality. Our findings indicated that the CF of extruded and pelleted feed was approximately 1334 and 1071 kg CO2 eq/t, respectively. Furthermore, the CFs of grass carp fed with extruded and pelleted feeds was 1876-2134 and 1928-2142 kg CO2 eq/t, respectively. The pro-duction of raw materials was the largest contributor to the CF of both feeds. If US soybeans were used, the CF of both grass carp feeds could be reduced by more than 15% compared with Brazilian soybeans. The reduction in the overall CF by using renewable energy sources such as photovoltaic cells would be similar to that of natural gas. The CF of China's freshwater fish feed is projected to reach 1.95 x 107 t CO2 eq in 2020, of which extruded feed and pelleted feed account for 20.32% and 79.68% of the total output, respectively. In this case, if extruded feed is used instead of pelleted feed and the feed conversion ratio is optimal (1.4-1.8), the proportion of freshwater fish fed with extruded feed should not exceed 21.05% of the total production of freshwater fish in order to reduce feed-associated CF.