Species mix and culture sequence
Based on scientific farming principles, production systems which have attained the status of technology and are suitable for large-scale adoption in the country
a) monoculture of penaeid prawn,
(b) monoculture of mullets, Chanos sp., Lates sp. and Etroplus sp.,
(c) biculture of penaeid prawns with mullets or Chanos sp., Etroplus sp., (d)
(d) biculture of fishes
(e) triculture of prawns and fishes of aforesaid species.
Based on ecological consideration and availability of stocking materials, a suitable species mix and culture sequence have been formulated for different coastal stretches along the east and west coasts of the country In pond under monoculture of prawn algal bloom develop during the summer season due to fertilization and supplementary feeding. To control this excessive algal concentration and to keep the pond ecology congenial for prawn growth, herbivorous species i. e. mullets or milkfish may be introduced in prawn ponds at a low stocking density of 500 to 1000 nos.jha.
This method is not only found to be effective in biological control of algae but also contributes substantially to enhance overall production of the pond.In biculture of fish and prawn, two crops of prawn and one crop of fish are usually obtained during a culture period of one year. Combinations other than that given can also be adopted considering the compatibility of the species, availability of stocking materials and other ecological factors.
Stock manipulation and stocking densities
By proper manipulation of stocking densities and cropping pattern, there are three methods of achieving high production viz.
(a) single stocking and single harvesting: In this method, fish and prawn of uniform sizes are stocked at a time and reared till they attain marketable size.
(b) single stocking and multiple harvesting: In this system, different size groups are stocked together and specimens both, fish and prawn, which attain marketable sizes are harvested and the rest are allowed to grow further.
(c) multiple stocking and multiple harvesting: In this system, fish seed of different size groups are stocked together and after a period of growth the species which attain marketable size are harvested and replenished by equal numbers of seed of the same species of smaller size groups so as to maintain uniform stocking density as planned at initial stage of culture.
Monoculture of prawn/fish
In monoculture of P. monodon, the stocking density of 50,000jha in case of postlarvae (12-24 mm) and 15,000-25,000jha in case of juveniles (40-50 mm) may be adopted. Whereas in the case of P. monodon, the suitable stocking rate is 40,000 to 70,000jha for 15-20 mm seed which is available in the natural collection. In both, the cases normal culture duration of 100-150 days will yield marketable prawns. But depending on the natural fertility of the prawn pond, much shorter or slightly longer duration of culture may also be tried for obtaining the desired yield
For monoculture of fishes i. e. C. chanos, M. cephalus & L. tade, a stocking density between 3000 and 5000fha with fry size of 60 to 80 mm may be cultured for a duration of 10-12 months for raising marketable crops. If the desired size is not attained in the first year, the culture duration may be extended to the second year. In monoculture of L. calcarifer, a stocking density of 3000fha is to be practised in slightly bigger impoundments with frequent flushing facilities so that sufficient forage fishes are allowed to enter into the pond along with tidal waters which serve as food for the growing Bhetki. If the desired size is not attained within a year, the culture operation may be extended to the second year
In monoculture of penaeid prawn, a net production of 250-350 kg of the crop can easily be obtained within 100-150 days. In three short-term crops a year, a total production of 1185 kg has of P. monodon has already been achieved at the experimental brackishwater fish farm of the Institute at Kakdwip. In monoculture of fishes i. e. C. chanos, M. cephalus, or L. tade, a net production of 1000-1200 kgfhafyr can be achieved. Production from the monoculture of L. caIcarifer is still better and varies within 2000-2500 kgfhafyr.
BicuIture and tricuIture production systems
Besides usual monoculture of prawns, biculture of prawns, prawn and fish, triculture of prawns and fishes may be undertaken. In biculture of prawns, only two penaeid prawns namely, P. monodon, and P. indicus are generally used and a production upto 500 kgfhafl20 days may be obtained.In biculture of prawn and fish, a fast-growing non-predatory and basically herbivorous fish may be stocked either with P. monodon or P. indicus. The most important combination may be P. monodon or P. indicus with Chanos chanos. Since C. chanos requires nearly 6 months to attain marketable size, the culture duration may vary from 140 to 180 days.
A production range from 1000-1200 kg/ha may be obtained. In triculture, one fish and two prawns or vice versa may be used and a production ranging from 500 kg/hato 1900 kg/ha may be obtained. In triculture of fishes, 3 fast-growing fishes may be selected depending on the availability of fish seed at the particular place of culture. The most common combination may be Chanos chanos, M. cephalus and Etroplus suratensis. Another combination is Liza parsia, L. tade and C. Chanos. In such a culture, production upto 1400 kg/ha may be obtained.
- Central Inland Fisheries Research Institute, Barrackpore