Freshwater aquaculture (2+1)

Unit 4 - Cultivable fish and their culture methods

4.1.1. Farming of carps
The distinctive features of carp culture are that the practices

• Tend to be semi – intensive
• Almost always use poly-culture
• May be integrated with other forms of farming (Integrated systems)
• Are carried out in ponds and pens but rarely in cages and raceways.

Poly-culture is thought to have originated in China. Polyculture is farming of two or more compatible species with different feeding habits in the same pond to maximize utilization of all the niches (food and space) of a pond. It maximizes the synergistic fish-fish and fish–environment relationships and minimizes antagonistic relationships. Under same level of management production will be generally higher in polyculture systems and more number of species can be grown for market than in monoculture systems.
A concerted experimental effort occurred in India to develop suitable polyculture system using both Indian and Chinese carps. The basic species combination in the Indian composite polyculture system was catla, rohu, mrigal, silver carp, grass carp and common carp. At a stocking density of 5000Nos., / ha (120-250 kg/ha) the yield was nearly 9 MT/ha/yr, when fertilized and provided with simple supplementary feed such as mixture of rice and oil cake. The polycutlure of Indian and Chinese carps together was termed “Composite fish culture”.
Despite experimental findings in both India and China farming practice tends to depend on two or three species of either Indian or Chinese carps. This trend is primarily influenced by consumer preference of indigenous species.
Both in India and China two or three species of either Indian or Chinese carps are polycultured. The dominate species in India is rohu and in China it is silver carp.
Over the last three decades carp farmers have developed their own protocols. This is best exemplified in Andhra Pradesh where only two species of Indian major carps namely rohu and catla are cultured. Rohu is the dominant species in polyculture which is stocked at 80% of the stocking density, catla being stocked at 20%. The pond area often exceed 1ha and the ponds are stocked with 6-12 month old (100-150g) juveniles@ 5000/ha. Ponds are generally fertilized with poultry manure and inorganic fertilizers. They are provided with supplementary feeds such as simple mixture of rice bran and oilcake. Production in Andhra Pradesh averages about 8000 kg/ha with a range of 5300-14620 kg/ha. Fish are harvested when they are more than 1.5 kg in size.
On the other hand, Chinese carps are grown along with common carp in China. There are also regional differences in Chinese carp culture. The most important difference is in the dominant species in polyculture. For example silver and bighead carps dominate in central China, while grass carp dominates in Southern China.
The wide range of practices adopted by the farmers makes it different to assess potential yields from different systems. For example in Andhra Pradesh where two operational systems are observed – one utilizing two species (Rohu and Catla) and other utilizing three species (rohu, catla and mrigal) gross yields ranged from 1730 to 14830 kg/ha/yr. There was no evidence to indicate that two or three species system performed better than the other.