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Acclimitation of post-larva to grow-out system.
Undoubtedly the received post larva will have differing water quality parameters (salinity, temperature, pH, alkalinity, hardness) to that within the grow-out system and so a period of acclimitation is required. The most effective method is that using acclimitation tanks (a station). Parameters, including post larval counts should be communicated from the hatchery prior to arrival. The ideal situation would be for the hatchery to pre-prepare the larvae to more or less the conditions in the grow-out tank.
The equipment required is as follows: thermometer, salinity refractometer, dissolved oxygen meter, pH meter, calculator, 3 1-litre beakers, two 100 ml beakers, airhoses and airstones, two 1000 litre capacity tanks (PVC), back up oxygen system, hose or plumbing for draining tanks to grow-out tank, freshwater and saltwater source, 500 micron filtered drain (for removing water in exchange), acclimitation report. Note: the calculation is for one million post larvae to be acclimitised in 2000 litres. If the time of acclimitisation is to be longer than 8 hours then the volume should be doubled (or the density halved) with all accompanying equipment.
Post larva will be normally transported at anywhere from 500 to 2000 per litre. Upon arrival each shipping bag should be inspected to determine the condition of the post-larvae. They should be swimming actively and exhibit good colour. The cephalothorax should be a yellowish or pinkish colour. Determine whether any of the bags contain a significant number of dead shrimp. These will be opaque or white. Record bags with problems and communicate with hatchery for possible credit. Randomly select four bags from the shipment for conducting a water analysis. open the bags and immediately measure the pH and dissolved oxygen. Place an airstone immediately in each bag and begin to aerate the water. Once aeration has commenced, measure the temperature and salinity of each bag and remove a small sample of water for ammonia analysis. If there is a suspect count from the hatchery then a count can be done at this point (or in the acclimation tanks later).
The bags should then be emptied into the acclimitation tanks accordingly. Water at the same temperature and salinity can then be added at a small volume initially to lower the density and an appropriate feed can be added (recently hatched artemia or flakes). The supplying hatchery normally would export the post-larvae with artemia in the bags as well as activated carbon as an ammonia absorber and EDTA as a flocculant. The hatchery might be in a position to send several extra bags with hatched artemia at high density and low temperature for immediate insertion into the acclimitation tanks with the post larvae.
Water exchange can be either by batch water exchange or by continuous exchange. Water quality (dissolved oxygen) and sufficient correct feed should be maintained throughout the process. The acclimitation rates in the following table need to be adhered to:
Salinity Change Recommended Time Allowed Recommended ppt per hour 32 ppt to 16 ppt 8 hrs 2 ppt / hour 16 ppt to 8 ppt 8 hrs 1 ppt / hour 8 ppt to 4 ppt 8 hrs 0.5 ppt / hour 4 ppt to 2 ppt 8 hrs 0.25 ppt / hour 2 ppt to 1 ppt 8 hrs 0.125 ppt / hour 1 ppt to 0.5 ppt 8 hrs 0.063 ppt / hour