*2.3.1. Suitable crustacean types*

combination of these two methods [19]. In this farming rice and aquatic species were started like synchronous farming, but the aquatic species are not harvested while rice species are harvested. It means that relay farming requires longer period for aquaculture. During rice harvesting the growing aquatic species were transferred to special ditches/ponds which are connected to channels/pools of the rice field and then restocking them in the rice field after filling up of water for further growth. It means this method requires additional rearing facility for transferring fish at the time of rice harvesting. Relay farming provides high amount of aquatic protein with high yield of rice crop with short duration. The drawback in this method is more investment and labor. The carp and prawn species are the most commonly used to

Worldwide integrated farming of aqua with irrigation is becoming popular to produce more yield and makes the farmers economically strong. It is well practised in the rainfed areas mainly in countries producing rice. The 86% of rainfed areas in Thailand produce rice [20] as is the case with Lao PDR [21] and Cambodia [22, 23]. Various types of aquaculture in the rice fields are in practice. The major aquatic species that come under finfish and shellfish are the cultural species used for integration with rice fields. Among finfish and shellfish, the two types of cultures brackish and freshwater species have importance to grow in RAF. But the selection of this species purely depends on the variety of rice growing. It is very particular that only certain rice species are productive in brackish water. The rice varieties of holding salinity tolerance and floating-stem (long-stemmed) were preferred for brackish water RAF. The brackish water effect is tidal on rice species holding salt tolerance and long-stem, since these species have the capacity to withstand even in salt water. Besides rice variety the selection of fish or crustacean cultured also play a role in RAF. The freshwater prawns like *Macrobrachium* species and brackish water prawns like *Penaeus monodon* and other species grow well in the rice fields. Most species of fin fish can grow well in rice fields. However, the farmers have to be careful about the selection of aquatic culture species and the variety of rice for integrated culturing.

Studies were focused on the stability of rice field ecosystem with rice monoculture and riceaquaculture [10, 24]. A survey by Xie et al. [10], with farmers cultivating rice with or without integrated aquafarming, revealed no difference in the yield of rice between the two farming for a period of 6 years. However, the temporal variation in the yield of rice is influenced by many factors such as year-round and year-to-year changes in climate, pest incidences, rice variety cultivation and the amount of pesticide used until harvesting [25, 26]. The usage of large amount of pesticides is responsible for temporal stability of rice yield in the case of rice monocultures, whereas rice yield stability is partly on the presence of aquatic species in riceaquaculture farming [10], since fish-aquatic cultural species act as biocontrol agent [27]. In the modern agriculture, the stability of rice yield is maintained through the extensive usage of pesticides and fertilizers [28, 29]. In contrast, the stable yield of rice is highly maintained by exploiting synergies between species to minimize usage of chemicals and is suggesting to the modern agriculture that rice monocultures need to be improved with addition of species for facilitating positive interactions between species and components. The interactions between

various components of RAF are presented in **Figure 5**.

produce protein in relay farming.

**2.3. Suitable aquatic species**

18 Aquaculture - Plants and Invertebrates

There are a number of crustacean species that grow in the rice fields as an integrated culture. The best example to explain this is the freshwater rice field crab that grows naturally in the rice fields of India. Besides crabs, there are other crustacean species like prawns, shrimps, lobsters and crayfishes that can also be grown in the integrated system along with rice with proper management [33], which is in practice in the coastal areas. Since the most profitable crustacean protein in today's world market is from shrimps or prawns, the production of these species is more profitable to the farmers especially the Indian and Asian conditions.
