It is unclear how widespread the system is in eastern India, or who the main practitioners are. In planning to adopt this system, it is important to study the agroclimatic conditions, and know what the main limitations and constraints are. A widespread system is the polyculture of small Indian major carp and tilapias in the extensive sewage fisheries of Calcutta where there have been major conflicts between absentee landowners who control the sewage-fed fishponds and landless people wanting to plant rice. Most of these fishponds, which used to extend over 40 km2, are managed to reduce the risk from heavy metal contamination of sewage and to produce small, live fish for poorer urban markets. This is a parallel activity to the use of solid waste and sewage water for the production of vegetables. This is not carried out by fish farmers and to some extent the horticulturists and aquaculturists are competitive for sewage.