Abstract: Abstract: In order to cut down energy consumption, heat loss and air pollution for water heating in indoor aquaculture system, a seawater-source heat pump system, which comprised 2 heat exchangers (namely I-stage exchangers) and a seawater-source heat pump and employed waste water as heating source, was developed and applied in an aquatic organism indoor nursing system. The onsite flow rate of waste water and fresh seawater in I-stage exchangers were regulated to 400 m3/h, respectively. The flow rate of waste water in the seawater-source heat pump was 20 m3/h, while the flow rate of fresh seawater increased from 10 to 20 m3/h during the onsite operation. The effectiveness for fresh seawater heating and the heat recovery of waste water by the seawater-source heat pump system were studied on site, and the amounts of energy consumption and carbon emission during the heating period were correspondingly calculated and compared with conditional coal-fired boiler heating approach. It showed that the heat-exchanging efficiency of I-stage heat exchangers was in direct proportion to the temperature difference of inflowing waste water and fresh seawater. When the inlet temperatures of waste water and fresh seawater were 10.3 and -1.9 ℃, respectively, the 5.8 ℃ increment of temperature in fresh seawater and 6.1 ℃ drop of temperature in waste water were observed. Additionally, with 14.9 ℃ inflowing waste water and 4.9 ℃ fresh seawater, the outlet temperature of fresh seawater increased to 9.5 ℃, while the waste water dropped to 10.0 ℃. The maximum heat recovery efficiency by I-stage exchangers from waste water was 59.5%. On the other hand, when the temperature and flow rate of inflowing waste water were not changed, the temperature increment of fresh seawater from the seawater-source heat pump was inversely proportional to its inflowing rate and temperature. With waste water of 14.9 ℃ as the heat source of the seawater-source heat pump, the temperature of fresh seawater increased from 7.3 to 18.6 ℃ at 10 m3/h and to 13.2 ℃ at 20 m3/h, which brought out temperature increment of 5.9-11.3 ℃. In the same case, the temperature of fresh seawater out of the seawater-source heat pump increased from 10.3 to 20.1 ℃ at 10 m3/h and to 16.6 ℃ at 20 m3/h, with temperature increment of 6.3-9.8 ℃. Accordingly, when the temperature of inflowing fresh seawater was 7.3 and 10.3 ℃, appropriate water temperature (15 ℃) could be obtained for aquatic organism indoor nursing by keeping the flow rate of fresh seawater at 15 and 20 m3/h, respectively. It was also found that the temperature drop of waste water in the seawater-source heat pump was about 6 ℃ during the operation, which gained the heat recovery efficiency of 40.7% for waste water. The coefficient of performance (COP) of the seawater-source heat pump was 5.03-5.52. In comparison with traditional coal-fired boiler heating approach, the integrated seawater-source heat pump system demonstrated significant drop in energy consumption (over 37.6%) and carbon dioxide emission (about 2 200 t/a). The payback period for the seawater-source heat pump system would be about 0.77 a. Therefore the seawater-source heat pump system has an obvious potential in energy conservation and carbon emission reduction in indoor aquaculture system.