Commercial Prawn Production
Harvest of ponds should be completed before morning water temperatures ever reach 60º F (15.6º C). Prawns can tolerate water temperatures to at least 55 to 58º F (12.8 to 14.4 oC), if the temperature decreases gradually over several days. When pond water temperatures below 68º F occur for a considerable part of a 24-hour period, growth rates of prawns are so low that keeping them in ponds for any extended period of time will essentially have no effect on increasing production.
At the end of the growout season, prawns may be either seine- or drain-harvested. For seine harvest, pond depth (or water volume) should be decreased by one third prior to seining. Prawns can be held in small mesh livecars and loaded with a crane-basket onto trucks. Those that remain after seining can be obtained by draining the pond to concentrate them in a large rectangular bar pit (ditch) that is deeper than the surrounding pond bottom. Prawns then concentrate there for seine harvest. Water in the ditch needs to be well aerated. Some prawns may remain outside the ditch harvest after draining and will have to be removed manually.
Harvest by complete drain-down is labor saving and more efficient and can be readily and effectively accomplished if ponds are properly designed with a smooth bottom and a slope that will ensure rapid and complete draining. Highly effective harvests have been achieved with properly constructed ponds because prawns living at water temperatures >68º F will follow the receding water and eventually travel through a drain pipe(s) into a collecting device or small collecting pond, generally located on the outside of the pond levee. There, sufficient aeration should be provided to the water to avoid stress and possible mortality as harvested prawns become concentrated. Adequate pond bottom slope and rapid drainage are critical to the efficient harvest of freshwater prawn. Ponds with very flat bottoms and small drains create many logistical problems relative to harvest.
Freshwater prawns are very hardy animals and do not die or diminish in quality when exposed to sunlight and soft muds for a short period of time. They can be collected in buckets or baskets and rinsed with clean water with few losses if they are not packed in extremely dense groups and not exposed to warm temperatures for more than 15 to 20 minutes.
Whenever possible, aeration devices for maintaining proper levels of dissolved oxygen should be located at the deep end of the pond adjacent to the drain basin area to minimize the accumulation of sediment there. Otherwise, aerators placed at the shallow end of a pond may produce depressions that will strand prawns as they follow the receding water during the drain harvest of a pond.
Selective harvest of large prawns by seining during a period of four to six weeks prior to final harvest has been practiced with the intent of increasing total yield from a pond during a growing season. Selection of the mesh size of the seine (one to two inches) will be dependent upon the desired harvest size of the prawn. Selective harvest may also be accomplished with properly designed traps. Prawns have been trapped using a wide array of traps traditionally designed for the harvest of crayfish. The reduction in population density caused by a partial seine or trap harvest results in an increase in the growth rate of the smaller prawns that remain. Through selective harvest, a freshly harvested product is available over a longer period of time. Insufficient research has been performed to determine conclusively whether a selective harvest practice is cost effective relative to a traditional, single bulk harvest at the conclusion of the growing season.
MSU Publications & Information
Other Freshwater Prawns Information