*2.2.2. Sequential/rice-aquaculture rotation/alternate farming*

Rice-aquaculture rotation is a simple method of farming where aquatic species were grown after harvesting of rice in the flooded fields without removing the rice stubbles. The water levels were shallow in the case of rice, whereas for aquatic species, water depth is raised. In this method more than one ASp were raised [19]. The depth for growing aquatic species in the field is raised well before the transplantation of rice seedlings with a moderate height of external dyke. However, the pesticides used for rice production degrades during interval between harvesting of rice and stocking of aquatic species. The rice stubbles in the water at the bottom of the field facilitate the growth of decomposing microbes which served as food

**Figure 4.** Different types of trenches in usage for rice-aquaculture integrated farming. (A) Diagonal trench, (B) crossed trench, (C) Y-shaped trench, (D) peripheral and one central longitudinal trench, (E) two equidistant transverses with peripheral trench and (F) latticed trenches.

for aquatic cultural species. The decomposition of stubbles enriches the water and soil with natural fertilizer utilized by the next cycle of rice where it helps to produce high yield.

The only limitation in alternate farming is about 20–60% loss of ASp due to piscivorous birds like herons and cormorants. Besides this, sequential rice-aquaculture farming has many advantages such as (i) no limitation for depth of water neither in rice cultivation nor in aquatic species culture, (ii) maintenance of adequate water levels provides sufficient dissolved oxygen and water temperature, (iii) rice stubble decomposition facilitates microbial food for aquatic species and fertilizer for the next cycle of rice for improved production, (iv) useful for monoand polyculture of aquatic species and (v) reduced attack of insect pest on rice fields due to interruption in their life cycle in rotation farming.
