Emergy evaluation of largemouth bass (Micropterus salmoides) aquaculture system in the Pearl River Delta, China

In this study, emergy analysis method was used to evaluate the benefits and driving forces of largemouth bass (M. salmoides) aquaculture system from ecological and economic points. For analysis, a number of different inputs have been identified and grouped in two categories: renewable environment resource inputs and purchased external resource inputs. The first group counted five natural, free and renewable inputs (solar radiation, wind, rain, earth cycle and river water), while the second group included eight external inputs (construction, fingerlings, electricity, feed, medicine, labor, rent and maintenance). Emergy indices for the largemouth bass aquaculture system calculated from the emergy evaluation, such as Transformity (TR), Emergy Yield Ratio (EYR), Environmental Loading Ratio (ELR), Emergy Exchange Ratio of Yield (EER_Y), Emergy Sustainability Index (ESI) and Emergy Index for Sustainable Development (EISD), were applied to characterize the resource utilization, environmental impact and the overall sustainability of the largemouth bass aquaculture system. These indices were compared with those of four other fish farming systems: the large yellow croaker (Larimichthys crocea) aquaculture system around Dongji Island in Zhoushan, China, the eel aquaculture systems on wetlands surrounding the Pearl River Estuary, China, the polyculture system of ophicephalus and mullet on wetlands surrounding the Pearl River Estuary, China and the dike-pond agro-ecological engineering system in Sanshui city of the Pearl River Delta. The results showed that the total emergy inputs was 4.51×10¹⁷ sej/(hm²·a). The renewable emergy inputs was 1.24×10¹⁶ sej/(hm²·a), which accounted for 2.75% of the total emergy inputs. The external emergy inputs was 4.38×10¹⁷ sej/(hm²·a), which accounted for 97.25% of the total emergy inputs. More than 70% of the emergy inputs into the largemouth bass aquaculture system was feed (77.33%). Labor was the second largest emergy input to the system (5.08%). The river water emergy was the major renewable environment resource input for largemouth bass aquaculture system (2.75%). The TR of this system was 2.18×10⁶ sej/J, EER_Y was 2.028, and EYR was 1.028. The ELR was 35.39, ESI was 0.029, and EISD was 0.059. The lower ESI with EISD and the higher ELR showed that the purchased external resource emergy inputs achieved a greater effect than renewable environmental resource emergy in largemouth bass aquaculture system, and the system had more dependence on purchased external resource emergy inputs, which indicated that the largemouth bass aquaculture system was less sustainable. The result showed that measures which reduced feed inputs and improved the feed utilization efficiency, such as using feed and additives with low feed coefficient, increasing feeding frequency, etc., could reduce the purchased external resources inputs, and then elevate the ESI and EISD of the largemouth bass aquaculture system. Integrated aquaculture was another method which could get the same result.