Better management practices for shrimp farming – Part I
Over the past few years, better management practices or BMPs have been identified and developed on the scientific basis to protect the environment, to improve the production and economic efficiencies with shrimp farming. These BMPs are also termed as good aquaculture practices. These practices are based on broader and widely accepted international principles for sustainable shrimp farming which is jointly developed by Food and Agriculture Organization of the United Nations, Network of Aquaculture Centres in the Asia Pacific, World Bank, Worldwide Fund for Nature and United Nations Environment Programme.
Here are the recommended BMPs at the farm level.
1. Maintain farmer unity through the formation of farmer group in the village or in the farming cluster. Collectively plan the farming activities. This will reduce many of the problems that farmers are facing.
2. Use Crop calendars appropriate to the district or farming area to determine the seed stocking time. All farmers must strictly follow this calendar system for successful crops for a long time.
3. Completely drain out the water from the ponds. This helps in removing the disease-carrying and carnivorous fish and crustaceans from the previous crop.
4. Completely remove the black organic waste from pond bottom especially from the feeding area. Organic wastes results from the decay of excessive feed; dead and decaying plankton and algae; and faecal matter from the shrimp and fishes. This may be present in thin or thick black layer form depending on the farming history of the farm. It releases toxic gases like ammonia and hydrogen sulfide in the tambak leading to stress and death of shrimps. It is easy to remove the black soil when it is in semi-dried condition. Displace the removed black soil away from the farm site or in the ditch created on the top of the embankment and cover it with good soil. Make sure that the displaced organic waste does not enter the pond again through rain washing. If it cannot be removed at one time, remove portion by portion in subsequent crops until the pond is completely cleaned. While removing the organic waste, make sure that the acid sulphate soil is not exposed to the surface. Ploughing on wet soil helps in reducing the toxicity from organic wastes.
5. Dry the pond bottom till deep cracks are formed in the soil. Sun drying kills fish and shrimps and their eggs in the soil. And also it helps in oxidizing the organic wastes thus reducing the toxic effect of the black organic waste.
6. Some farms may have acid-sulphate soils. Acidic soil causes high mortalities of shrimp and fishes, stress the shrimp and fish thus slowing down the growth rate and causing a disease outbreak, it causes poor algal bloom and depletes the oxygen in the water. Therefore such farms are highly risky for shrimp farming and increase the pond maintenance costs. Check the pH of the soil using Soil pH meter. Soil should be wet when using the equipment. If the pH is below 7 then it is called acidic soil. Do not plough on acidic soil. Wash the soil by water intake and drain for 2 to 3 times to reduce the soil acidity. Use proper quantities of dolomite or agriculture lime to neutralize soil acidity. For example, if the soil pH is 5 then use dolomite at a dosage of 1 ton per hectare.
7. Fill the water using the double layer of fine mesh water filter nets at water inlet points. This avoids the entry of wild fishes, shrimps, crabs and other animals to the pond. After filling the pond, hold water for 10 to 15 days before stocking the seeds. This will stabilize the water condition and makes the shrimp seeds comfortable in the pond. If the farm has water reservoir, then hold the water in the reservoir for 7 days before pumping it to the grow-out pond.
8. Maintain at least 80 cm deep water in shallowest part of the pond. Shallow water depths are highly stressful to shrimps due to quick change in temperature and other water conditions.
9. Do not use Pesticides. It is banned in aquaculture. Pesticides will enter and remain in the body of shrimps and fish for long time. And when these shrimps and fishes are consumed cause health problems in humans. If necessary, use saponin at a dosage of 100 kilogram per hectare.
10. Transparent water for prolonged time is bad for the crop. Transparent water leads to development of benthic algal mat which after certain period dies and releases toxic gases in the water. Therefore stabilize the plankton bloom to get green or brown colored water before stocking the shrimp seeds. Apply 25 kg per hectare of SP-36 and 10 kg per hectare of urea to the water for 2-3 times with a gap of 2-3 days after each dose. Also use dolomite at a rate of 100 kg per hectare after 2 days of fertilizer usage. Do not apply lime and fertilizers together. Do not heavily fertilize the water to get dark green water. It will reduce the oxygen in water during night time thus suffocating the shrimps. It is one of the reasons for poor survival rate of shrimp seeds.
11. All the farmers in the village or farming cluster should try to stock same batch of seed. Stocking different batches of seed from different hatcheries or nurseries should be avoided. This practice will prevent the cross-contamination of disease and gives the uniform coloured and sized shrimps for the market.
12. Stock the shrimp seeds only one time per crop following the crop calendar. Do not continuously stock the ponds with new batches of seeds.
13. Always purchase shrimp seeds from a well-maintained hatchery or certified hatchery.
14. Prefer PL-12 stage or older. The total body length should be more than 12 millimetres. Smaller sizes of seeds may not be ready for stocking and may quickly die in the pond.
15. Shrimp seeds should be uniform in size and colour. Seed with red, blue or green colour must be rejected.
16. Shrimp seed should be strong and active. To test this, collect about 500 seeds from the bottom of the hatchery seed tank and pour in a round tub. Stir the water. Wait for 2-3 minutes. If many seeds concentrate in the centre without any movement then do not select that seed batch.
17. Shrimp seed should pass a salinity stress test. To do this, collect about 50 seeds in a glass with hatchery tank water and pour equal quantity of drinking water. Wait for 3 hours. If more than 90% of the seed survives, then select the seed batch.
18. Shrimp seed should have full gut and well developed hepatopancreas. And they should be clean and without any damaged or missing legs. To see this, collect 10-20 seeds. Observe them under a magnifying glass or microscope. The gut should not be empty. Hepatopancreas should not be small and light in colour. The body surface should not be dirty, legs should be intact and should not be blackish. If these signs are found then reject the seed batch.
19. Seeds must be tested for diseases like white spot virus and MBV. Virus related disease can cause mass mortality of shrimps in tambak. Collect about 100 seeds and send it to a shrimp health laboratory for disease testing. Do the PCR test. The seeds should be negative for white spot virus by PCR test. Similarly PCR can be used to test other diseases like MBV, TSV etc. If there is no laboratory facility nearby, then dot blot test kit can be used to test for viral diseases. If double bands appear in the kit then it is positive for disease. Therefore reject the seed batch. If single band appears in the kit, it means seed is without any big quantity of virus. Hence the seed batch can be purchased. PCR test is more accurate or sensitive than dot blot test. MBV infection can be easily tested by staining method and using simple microscopy it can be detected. If MBV infection is very high then reject that seed batch.
20. While packing the seed batches, do not mix the seeds from different hatchery tanks.
21. Salinity of seed tank water and pond water should be the same and should not differ by more than 5 ppt. Therefore prior to packing the seed adjust the salinity of the seed tank water to the salinity of pond water. Start adjusting the salinity of hatchery tank water when seeds are at PL-10 stage and complete the process of adjusting the salinity at least one day prior to seed packing.
22. Seed bags should have enough oxygen. Volume of the oxygen should be at least 3 times more than that of water.
23. Each bag should have about 1000 PL or 1000 PL per litre of water. Do not pack with high seed densities.
24. Transport the seeds from hatchery to the farm site as quickly as possible preferably within 6 hours. If transportation time is longer, slightly reduce the temperature of the water using ice and transport in thermo cool boxes. Transport during evening or early morning period in enclosed vehicles. Avoid transportation during 7 AM – 5 PM.
25. Seeds should be released in to the ponds during cool hours of the day. That is after 6 PM or before 8AM. Release the seeds in deeper parts of the ponds and not in shallow water. Acclimatize the seeds to tambak water before releasing. To do this, keep the seed bags floating in water for about 30 minutes for temperature adjustment and then open the bag and slowly pour small quantities of the pond water over next 30 minutes and then release the seeds to the pond.
26. While stocking the seeds, there should be a good and stable plankton bloom with green coloured water. Avoid stocking in transparent or thick green water.
27. Do not purchase the juveniles from poorly managed commercial nurseries. It leads to high chances of importing the disease. Farmers should try to maintain on-farm nurseries within their ponds. Also they can organize a community nursery managed by farmer group.
28. Nursing period should be ideally for 2 weeks in earthern ponds. If hapa is used, then nurse for a maximum of 7 days. Tie the hapa properly inside the tambak so that it is not taken away by the air breeze.
29. Always use high quality pellet feeds from the day of seed stocking. Do not feed raw or boiled meat, fish, shrimps, crabs or snails. Do not use poultry or cattle feed in shrimp ponds. Do not mix any chemicals especially antibiotics with the feed. Always store the feed bags in dry and dark place to maintain the freshness. Do not use old and spoiled pellet feed.
30. Determine the feed pellet size based on the size of shrimps. When shrimps are small then use small sized pellets. Increase the size of pellet feed as the shrimp grows. Feed quantity on daily basis should not exceed the demand from the shrimps or the standard feeding table. Excessive feed is not eaten by shrimps. It will decay at pond bottom and releases toxic gases which creates stressful condition to shrimps. Use of feed check trays to estimate the feed demand by shrimps. Check the shrimps 2 hours after feeding. If the gut is empty then feed again. Use 4 check trays for each pond for better accuracy in estimating the feed demand. For initial 60 days feed at least 2 times a day and after that feed for 3 times a day. Spread the feed all over the pond using boat or floating device, not just spread on the sides of the pond. Check the pond bottom soil on regular basis and avoid feeding in areas with black and badly smelling soil.
Source: Indonesian Aquaculture