Optimization of the rice-fish coculture in Qingtian, China: 1. Effects of rice spacing on the growth of the paddy fish and the chemical composition of both rice and fish

Abstract

The sustainability of Global Important Agriculture Heritage System (GIAHS) such as the Qingtian rice-fish coculture system relies heavily on the good economic return that ensures the willingness of farmers to adopt, which in turn relies on the effectiveness of the technology. The dynamic conservation concept makes it possible for each GIAHS project to be optimized in technology while overall systems are conserved. To reach this goal, we compared the effects of three rice planting densities (20 cm × 30 cm, 30 cm × 30 cm and 40 cm × 30 cm) on both the fish growth performance and the rice productivities in this study. In one hand, the survival rate (SR), specific growth rate (SGR), amino acid (AA) and fatty acid (FA) of the fish (Cyprinus carpio var. color) in paddy field under three rice planting densities were compared. In the other hand, the rice yield indicators and rice stem characters were also calculated and compared among the different rice planting densities. The results showed that the SGR of fish reached the highest (4.54 ± 0.03) % in the medium rice density group (i.e., the 30 cm × 30 cm group), which was extremely significantly higher than that in the high density (20 cm × 30 cm) (3.62 ± 0.04) % (P = .001). However, the survival rates of fish were not significantly different among treatments (P = .298). The content of essential amino acid (EAA) in fish muscle under the high, medium and low rice cultivation densities were (37.35 ± 1.07) %, (37.35 ± 0.27) %, (32.20 ± 1.29) %, respectively. The first limiting amino acid was Met; the the total essential amino acid (TEAA) and the essential amino acid index (EAAI) in the medium and high density were all slightly higher than those in the low density. There were no significant differences in rice yield indicators among the treatments (P = .687); the number of effective panicles in the low density was significantly higher than that in the high density (P = .000), and panicle setting rate in the low density was significantly higher than that in the medium and high density (P = .038). In summary, the fish can obtain a faster growth rate while ensuring the rice yield in the rice density of 30 cm × 30 cm.