*2.3.1.2. Crab production*

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

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 specific time of spray at which crabs stay in burrows. Proper water management prevents the crab from escaping from rice fields. The average crab protein produced in rice-crab system is approximately 600 kg/hectare. The systematic management of crab culture changes the farmers socioeconomic status than the shrimp/prawn culture alone [39, 40] in addition, these crabs are more eco-friendly and grow easily in polyculture with other species [41, 42]. The only limitation in crab culture is limited availability of wild seed and is overcome by establishing crab hatchery industry to protect natural broodstock for continuous supply of seed [43]. The sequential or synchronous farming is the adaptable system for rice-crab culture, which depends on type of crab species growing.
