Effects on rice grains cadmium reduction and the characteristics of rice and fish in rice-fish coculture system

It is urgently necessary to produce low-cadmium (Cd) rice in Cd-polluted paddy soil. Integrated rice-fishing culture is an efficient complex ecological agricultural production mode, which combines the culture of rice with culture of economic aquatic animals, owning both economical and ecological benefit. In order to investigate the control efficiency on Cd accumulation in rice in the rice-fish coculture system, the newly hybrid crucian carp WR-Ⅱ Carassius cuvieri (♀) × C. auratus var. red (♂) (♀) × C. cuvieri (♂) was used as an example in the rice-fish coculture system, and the cadmium (Cd) concentration in rice grains, WR-Ⅱ and environmental medium were compared between the rice-fish coculture system and the rice monoculture system, as well as the quality traits of rice grains and the characteristics of WR-Ⅱ were analyzed. The results showed that the average weight of WR-Ⅱ (331.4±74.3) g in the rice-fish coculture system increased by 1.7 times compared to the fingerling (133.1±22.4) g; there existed no significant difference in the nutrient quality traits of rice grains between the two culture systems; the average value of total soil Cd concentration (0.472 mg/kg, pH=5.5) was a little higher than the pollution threshold (0.40 mg/kg, 5.5≤pH≤6.5), and there was no significant difference observed in the total Cd concentration in paddy soil and in the soil pH between the two culture systems; a low level of Cd accumulation (0.060±0.032) mg/kg was found in viscera of the WR-Ⅱ, while this value in fish muscle was lower than the minimum detection limit value (0.003) mg/kg for Cd; the average Cd concentration in rice grains in the rice monoculture system was 0.311 mg/kg (0.239-0.381) mg/kg, reaching 1.6 times of National Food Safety Standards Limits of Cd for Foods in China (0.2) mg/kg; while this value (0.034) mg/kg in rice grains in the rice-fish coculture system was much lower than 0.2 mg/kg, and was down 89.1% compared to that in rice monoculture system; there was significantly positive correlation (P<0.01, r=0.802) between the Cd concentration in rice grains and total soil Cd concentration in rice monoculture system, but not in rice-fish coculture system. Our results indicated that the WR-Ⅱwas a great species for rice-fish coculture system, which can inhibit the biological activity of Cd in soil, and in turn effectively reduced the rice in Cd uptake in this system, yielding low Cd and quality rice grains and fish, as well as outstanding economic benefits. The results of this study provide useful guidance and important data on Cd accumulation in rice for the promotion and development of integrated farming of rice and fish.