World Aquaculture 59 bicus) and African magur (Clarias gariepinus), an illegal entry, were being stocked with the carps, often with disastrous results. Tilapia being a prolific breeder and African magur being a voracious feeder caused loss of biodiversity of indigenous fish (Goswami et al. 2004). Role of Fish on Paddy The culture of fish in paddy fields generally benefits rice cultivation, resulting from better aeration of water and greater tilling from the movement of fish. The excreta of fish increase the fertility of soil. Fish also feed on harmful pest weeds and insect larva, which are harmful for paddy. Approach for Environmental Integrity and Food Safety Owing to the new trend of increasing concerns of the public about environmental integrity and food safety, many traditional food production systems including rice-fish culture, are confronted with new and more challenges. The means of producing high quality and safe rice and aquatic products through environmentally friendly approaches have become the focus of the development of modern day rice-fish culture. To ensure environmental integrity and food safety, many new technologies were introduced to the farming systems, such as the use of formulated bio-fertilizer and micro agent for water manipulation. In many areas, traditional ricefish culture has gradually transformed into organic food production systems. The organic rice and aquatic products not only bring the farmers more income, but also contribute to holistic rural development. Concurrent Rice-fish Farming Systems Culture of fish concurrently with rice during more or less the same production period is a most typical rice-fish symbiotic farming system. Therefore, the potential ecological and economic benefits of rice-fish integration are assured. Accordingly, specialized earthworks to modify the rice fields to meet the requirements of both rice and fish are needed. The suitable species for culture are those that do not require a long period to reach marketable size in grow-out culture. Concurrent rice-fish farming requires good engineering earthwork of the rice field. Major earthworks for preparation of rice field include reinforcement of field ridge. The rice field ridge should be at least 10-20 cm higher than the maximum water level in the rice field. The rice field must be seepage free. Peripheral and central crossing trenches are constructed in the rice field. The peripheral trench is usually 80-100 cm inside the rice field ridge to avoid escape of cultured animals. The trench is normally 50100 cm wide and 60-80 cm deep. A central fish pit (5-6 m² and 1 m deep) connected to the trench is sometimes dug in the central area of the rice field in large rice plots. The total area of fish trench and pit usually accounts for 10-15 percent of the rice field area to maintain more or less the same unit production of rice. In concurrent rice-fish culture systems, the yield of fish usually ranges 300900 kg/ha. The most important management aspects in concurrent systems include water management and use of pesticides and fertilizer. While meeting the requirement of rice at different stages, minimum water depth should be maintained for culture of animals in trenches and pits, 30-50 cm depending on species and weather conditions. Pesticides should not be used just before the rain. It is important to avoid the pesticides getting into the water when spraying. Organic fertilizer is preferred if fertilization is needed. Use of ammonium fertilizers should be avoided as it often leads to high ammonia level in water, which is toxic to cultured animals. Alternate Rice-fish Farming Systems In some rice-fish culture systems, instead of concurrent rice-fish culture, rice plantation and fish culture are conducted alternately in the same field. Rice plantation and fish culture may be conducted alternately by crop or annually. Compared with concurrent rice-fish culture systems, rice and fish do not have a close symbiotic relationship in alternate farming systems. However, alternative rice plantation and fish culture are beneficial to each other in many aspects. Alternative rice-fish culture is relatively easy and does not require extensive earthwork to modify the structure of the field. It is more suitable for fish species that require deep water and a longer culture period. The major requirements to conduct alternate rice-fish farming include reinforced rice field ridge, increased height of the field ridge (1 m), and a seepage free ridge. The alternate rice-fish culture usually includes one crop of rice followed by one crop of fish within a year. The fish production usually ranges between 1,500 and 3,000 kg/ha or even higher depending on the fish species and feeding. The stocking of fish is usually carried out immediately after the preparation of the field when the rice is harvested in October. The fish is usually harvested in June before transplantation of rice seedlings. In both concurrent and alternate ricefish systems, water inlet and outlet are positioned diagonally and well fenced with screens of appropriate mesh-size depending on stocking size of the cultured animals. Benefits of Rice-Fish Culture The North-Eastern states have low income sources and majority are farmers. Paddy cum fish farming gives them the ability to utilize fully their available resources. It can also serve as an off-season occupation for farmer and boost productivity and income earn-
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