*2.3.1.3. Crayfish production*

*2.3.1.1. Shrimp/prawn production*

20 Aquaculture - Plants and Invertebrates

*2.3.1.2. Crab production*

Shrimps are grown in brackish water, whereas prawns grow in freshwater. The shrimp production is done with the fields of holding salty water located in west coast and deltaic areas of eastern India where the salt-resistant rice varieties are grown. Due to limited availability of salt water, only one crop (integrated rice-shrimp farming) is grown mostly in the months of July to September every year. The channels are arranged to control the water supply into the field or pond during harvesting of rice, and the shrimp is protected in the ponds/trenches. At this stage, rice field consists of substantial number of shrimp larvae having less water. The shrimp harvesting in this case is usually done after 3 months of rice harvest. To clearly say the method followed to culture rice and shrimp is through alternative system (semi-intensive monoculture) with few modifications and balanced diet supplied during the culture. The average production rate of shrimp per hectare in this method is 1440 kg. *Penaeus monodon* is the most common species grown in this type of culturing. *Penaeus merguiensis, Penaeus indicus* and

The most popular species of freshwater prawn grown in the integrated rice-prawn culture is *Macrobrachium rosenbergii* (*M*. *rosenbergii*). The monoculture of *M. rosenbergii* in the rice fields is in practice in North Kuttanad, where almost 248 hectares are cultivated integrated riceprawn culture in a year [34]. Like rice-shrimp farming, the alternative system of culturing is adapted for rice-prawn culture (semi-intensive monoculture). The productivity of prawn monoculture with rice is around 700 kg/hectare. On the other hand, the polyculture of prawn (*M. rosenbergii*) along with fish (*Catla catla*, *Labeo rohita* and *Ctenopharyngodon idella*) in the rice fields is also in practice, where the productivity of prawn is 285 kg/hectare, which has almost two times less production of monoculture of prawn in the integrated system. The yield of

*Penaeus monodon* with mixed cultures in the rice fields is about 2135 kg/hectare [35].

More than two decades ago, the role of indigenous technology in the production of rice-crab culture is well described [36]. The crabs *Oziotelphusa senex senex* or *Parathelphusa hydrodromus* are commonly called as 'freshwater rice field crabs' since their occurrence is naturally in the rice fields. Besides this *Eriocheir sinensis* (Chinese mitten crab) and *Scylla serrata* (mud crab) are the major crab species used for rice-crab integrated farming. Mitten crab is a famous cultural species of China, whereas the mud crab is the most economic crab identified and grows throughout the world. Both these species grow in saline water and are cultured along with salt-resistant rice species in the case of integrated culture. *Scylla serrata* is popular in Asian continent. This crab culture is picking up in the Indian states such as Kerala, Tamil Nadu, Karnataka, Andhra Pradesh, West Bengal, Maharashtra, Odisha, Gujarat and Union territories. However, the crab culture is influenced by many factors, including environmental,

Crabs depend on naturally available food in the rice fields. Anyhow, supplementation of external feed is needed during fast-growing periods. The management of rice-crab culture is much easier than other RAFs. But the only management aspect that needs to be addressed is regulation of pesticide usage. Since the usage of pesticides is unavoidable for rice yield, it can be managed by selecting less toxic pesticides with a method of spray on rice stems and

*Metapenaeus ensis* are alternative species to grow in this type of system.

biological, physical as well as socio-economic factors [37, 38].

Similar to crabs, crayfishes are the strongest crustaceans that tolerate unfavorable conditions than other species. The most common species used in rice-crayfish integrated system are *Procambarus clarkii* and *Cherax quadricarinatus*. The rice-crayfish culture is common in Southern United States (*Procambarus clarkii*) and in Australia (*Cherax quadricarinatus*). The adult crayfish is used as broodstock to get seed in the ponds. The broodstock is released into field after 1 week of rice seedling implantation. On the other hand, the crayfish seed is also obtained from hatcheries. Besides this the seed also obtained from the rice-crayfish integrated system after harvesting, where the adult crayfish produce juveniles which are used as seed for immediate culture. Unlike other crustaceans rice-crayfish culture is also done with sequential farming. In this system before 2 weeks of harvesting the rice, the water is drained to facilitate crayfish to make burrows [44]. Watering the field after harvesting leads to growth of ratoon crop (occurrence of regrowth from rice stubbles) and facilitates the growth of insects, zooplankton, worms and molluscs, which promotes the direct growth of flushed out crayfish from the burrows [45]. The optimum weight for harvesting crayfish is about 15–60 g. The average yield of crayfish in this system is about 1960 kg/hectare [46].

Many other aquatic species can be integrated with rice culture. The typical integration of aquaculture with rice system followed in Asian countries is presented in **Figure 6**.
