Nursery ponds are very important for producing fish seeds/fingerlings. Common carp (Cyprinus carpio) nursery pond management in Rajshahi city was observed for a period of 6 months in 2009. Findings are briefly described here.
- Pond collection: Majority farmer collected ponds through lease system. Lease duration was generally 3 years and pond collection cost was reasonable.
- Bottom and dyke repair: Bottom and dyke were repaired carefully before stocking the fry in nursery pond.
- Control of aquatic weed: Traditional methods were followed (manual and using simple device like bamboo stick, straw made twisted rope etc.) to control aquatic weed.
- Removal of unwanted fish or other aquatic animal: Rotenone and Phostoxin (gas) tablets were used for removal of predatory and unwanted species of animal.
- Rotenone is generally available as powder forms. Commercially found as Fish Tox and Atox.
- Phostoxin or Gas tablet is used to kill different types of pests. Each tablet is weighted 1-3 gm. This is very effective to remove predatory and unwanted fishes and other pests of the pond. Farmers apply this tablet in the water body and water was agitated by using net.
- Liming: The farmer used lime at the time of pond preparation. Most common method of lime application was identified as diluted lime and applies it by throwing.
The action of lime treatment is beneficial in several respects.
- Acidity of water is corrected
- A strong pH buffer system is established
- Decomposition of organic matters of deposits on soil takes place
- Liming serves as disinfectant against fish disease
- Aeration improvement in humus occurs
- Liming precipitates harmful metallic compounds
- It helps in mineralization of ions
- Resultantly, in the presence of calcium as a nutritive agent, high production of phytoplankton and zooplankton gets stimulated to fulfill the need of nutrition by growing fish fry.
- Control of aquatic insects: The farmer used sumithion to remove aquatic insects from the study nursery ponds. Sumithion was a popular liquid insecticide in study areas and found in local markets. It was very effective to remove “Haspoka” and “Argulosis”. Sumithion was applied at the rate of 2.5 liter/ha.
- Fry collection: The farmers collected common carps fry from government hatchery located at Aambagan, Upasohar, Rajshahi. The newly hatched fish larvae were transported mainly by rickshaw in a polythene bag with oxygen supply.
- Water toxicity test: The farmer tested toxicity of water before stocking the fry in the pond.
- Natural food testing: Direct eye observation was applied for testing natural foods in ponds.
- Releasing: 22.72 g of newly hatched common carp larvae were released in 1 decimal pond. The farmer stocked fry in the early morning (around 6:30 am). Releasing method of fry in the nursery pond was simple. The polythene bag containing fish fry was immersed in the pond water and after 2 minutes bag was opened to release the fry.
- Pond monitoring: The farmers monitored their pond regularly and observe water color, availability of natural food and growth of stocked species.
- Supplementary feeding: Supplementary feeding in nursery pond is essential if high stocking density is maintained. In the studied ponds, wheat flour (at 22 g/ha) and mustard oil cake (at 22 g/ha) were used for feeding the stocked fishes.The choice of supplementary feed is related to these considerations:
- Readily acceptable to the growing fry and easily digestible,
- Possession of high conversion value and fish food should be easily transportable,
- Easily and abundantly available and have good keeping quality, and
- Should be available in low cost.
- Harvesting: After one month of rearing, the fish seeds/fingerlings were harvested. Pond operator hired labor for netting. They used net made by nilon and one special type of net which is locally called “Mosari jal” for harvesting which is generally done in the early morning (around 6:00 am).
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