Construction of pen culture
a. Site selection:
- Shallow region along the banks of lakes and reservoirs.
- Location determined by consideration of factors like water quality, water depth and water circulation.
- Lake or reservoirs should be relatively flat and free from large stones and logs.
- Maximum depth must be less than 2 m.
- Sites subjected to high water currents, storms, landslides and extreme climatic conditions should be avoided.
b. Pen size, structure and construction:
- Small-seized pens usually allow for higher fish yields, lower production costs and easier management.
c. Wall net:
- Net used in pens are made of 10 mm polyethylene threads with a mesh size of 2-2.5 cm.
- The height of net above the maximum water level of the lake should be about 90-120 cm.
- Chinese use two layers of net enclosures of same mesh size.
- The inner core is used for culture of fish and the outer enclosure is used to prevent the escape of fish.
d. Bamboo or wooden stakes:
- Used to support the wall net.
- Bamboo poles of 8-9 cm in diameter or wooden poles of 3’’ x 4’’ are driven into the mud to a depth of 30-40 cm.
- The main stake, used for hanging the wall net, is spaced every 1.5-2 m.
- This should be about 60 cm below the silt soil bottom.
e. Concrete blocks and rod anchors:
- Concrete blocks of 3-5 kg are to be put into the bottom line of the wall net to prevent fish escaping near the bottom.
- Sometimes U-shaped iron anchors are places into 20 cm depth of silt with a distance of 0.5 m for reinforcing the pen.
f. Suitable species:
- Silver carp, bighead carp and grass carp are popular.
- Using common carp is risky because of its bottom dwelling habit.
- Rohu is most preferrable.
g. Stocking density:
- 5000-10000/ha.
- The average weight of fingerlings stocked is 20-25 g.
- Formulated feed should be given at the rate of 4-5% of total body weight.
- No fertilization is needed in pens.
h. Care and management:
- Regular monitoring, cleaning and repairing of wall net and poles.
- Regular growth check of fish, at least once at a month.
- Regular water quality monitoring.
- Monitoring of feeding behavior.
- Adopt multiple stocks and harvesting system.
i. Harvesting:
- Done by seining.
- Special care should be taken to return to the pen any undersized ones in the net.