Before we go into the detailed methodology of fish culture in the rise fields we shall briefly look at the various types of aquaculture in the rice fields. As already referred to both finfish and shellfish (shrimps and prawns) have been used in culture in the rice fields. Again both freshwater and brackish water culture are prevalent, with obvious differences in the type of rice cultured - salinity tolerant and long-stemmed (floating), in the case of rice cultured in brackishwater under tidal influence - and also in the types of finfish and prawns cultured. The prawns are used mainly in culture in brackishwater regions, but freshwater prawns (cf. Macrobrachium spp) might also do well in aquaculture in the rice fields, but tests at this level are few.
The type and technique of growing fish would depend much on the local conditions. The Principal factors involved, according to Schuster et al (1955) and Coche (1967) are climatic and other local conditions, fish species available, rice variety cultivated, method of rice culture, fertilization, type of fish culture method, supplementary feed etc.
We shall list out here the types of culture systems as pointed out by Coche (1967). The systems can be classified according to the origin (source) of the fish or the relation of fish culture to rice crop. Coche (1967) recognizes 4 categories according to the origin of fish:
Harvesting wild fish which have entered the field through water courses.
Increasing the wild crop in the field by introducing new fish directly into the field or indirectly in connected ponds, wells etc.
Trapping wild fish admitted into the field with tidal water (generally brackishwater - the technique of admitting fish is not so passive as it appears - the water flowing into attracts fish by rheotactic stimulifurther often lights are used at the sluices to attract fish and prawns phototropism and photokinesis).
Trapping fish (as in ‘3’) and allowing them to grow before capture.
As obvious, these 4 can be grouped into captural (1 & 3) and cultural system (2 & 4).
Captural system involves no selective stocking, the fields being initially used for stocking - these is no cultural practice as artificial feeding and fertilization for fish per se involves, (extensive system).
In cultural system the field is deliberately stocked like a culture pond, and is often followed by artificial feeding and other culture practices (intensive) Depending on the relation of rice and fish crop, fish culture may be of different types:
The fish and rice production can be simultaneous, when the two are grown together (contemporaneous), “Rizipisciculture” and alternate when rice crop and fish crop are grown alternately in rotation.
Alternate or production by rotation can be of different types
Certainly these can be practised/changed according to the exigencies of circumstances.
Concurrent growing of fish and rice is known as rizi-pisciculture (Paddy or rice-cum-fish culture) in the traditional sense. Both concurrent culture and culture in rotation have their advantages, and disadvantages, which will be discussed separately hereunder.
The last type of classification of culture methods is based on the size of the fish harvested.
This culture will depend on the availability of water and depth of water in the rice field. The duration of rearing is usually short, but with trenches and refuges, for fish to take shelter, longer durations of culture can be had. In Japan, the fish are taken and kept in holding ponds and liberated again in the rice fields thus extending the rearing period for several years. It must also be pointed out that the short time available for growing fish enables the rice fields to be used as a nursery (fry to fingerlings - perhaps also hatchling to fry) - here the paddy field would be of great help due to the paucity of space otherwise experienced for fry and fingerling production (cf. Pond culture lectures).
In all systems, however, rice is the primary crop and fish culture is secondary or complementary. Perhaps this is due to the well established technology for rice and also the fact that it is the rice grower who has taken to fish culture.
