Both surface and subsurface water can be acceptable for crawfish farming. Well water is free of predators but has a limited discharge capacity and higher pumping cost. Surface water is less costly to pump, but may not be reliable in quantity or quality. Surface water also can contain predatory fishes that must be removed.
Passing surface water through small mesh screens can effectively remove most fish and aerate the water (Fig. 3). Small fish not retained by screens may compete with the crawfish for food items and prey upon small crawfish.
Pools or puddles remaining when the pond is drained in summer should be treated with a fish toxicant. Pumps, motors and pipes must be matched to the system and to each other to obtain the most efficient performance. Lift should be minimized as much as possible to reduce pumping costs.
Water quality:
The quality of water required to produce crawfish is similar to that required by most warm-water aquatic animals. Important water quality variables are dissolved oxygen, pH, total hardness, total alkalinity, ammonia, nitrite, iron, hydrogen sulfide, and salinity.
Dissolved oxygen is the most important factor in water quality. It should be maintained above 3 parts per million (ppm) for optimal crawfish production. Oxygen deficiency is corrected by replacing pond water with fresh, oxygenated water or by recirculating water with pumps or mechanical aerators.
Pumping water through an aeration screen divides the water into small droplets and aids in oxygen transfer. Well water can also be aerated by exposure to air as it travels through supply ditches.
Water pH should range from 6.5 to 8.5 at dawn; both total hardness and total alkalinity should range from 50 to 250 ppm as calcium carbonate (100 ppm is optimal). If the pH, hardness, and alkalinity are low, incorporate agricultural limestone into the pond during the next dry cycle to increase the levels of calcium carbonates.
Un-ionized ammonia and nitrite are toxic to crawfish at concentrations higher than 2 and 4 ppm (as nitrogen), respectively. Concentrations this high are unlikely in well water or crawfish ponds because crawfish production intensity is low and ammonia is rapidly taken up by phytoplankton and aquatic plants.
Iron and hydrogen sulfide are toxic to crawfish at concentrations often found in well water, but the two compounds may be lowered to non-harmful concentrations when well water is oxygenated.
Where iron and hydrogen sulfide concentrations are high, it may be necessary to place a supply ditch or pond between the well and the crawfish pond. This will allow the iron to precipitate and hydrogen sulfide to dissipate.
Crawfish farmers in coastal regions should monitor tidal influence on surface waters. Crawfish tolerance to salinity is directly proportional to crawfish size. Newly hatched young may die at 8 parts per thousand (ppt), while adult crawfish can tolerate salinities up to 35 ppt (sea water) for a short time. Salinity affects vegetation at much lower concentrations.
Crawfish ponds should not be located where salinities higher than 5 to10 ppt are likely to occur.
Water quantity:
The quantity of available water often limits crawfish culture. Intensive production requires a pumping capacity of 70 to 100 gallons per minute per surface acre. This rate is needed to exchange all the water in the pond over a 4- to 5-day period, especially in the early fall when the pond is flooded onto decomposing vegetation.
Adding 4 to 6 inches of water at flood-up rather than the full, harvesting depth of 12 to 18 inches will reduce the amount of water needed for oxygen management. The depth would then be gradually increased as water temperature cools.
A pond with dense vegetation may need seven to nine water exchanges per season to maintain good water quality. If poor quality water is discharged, total water usage for the season can be as high as 10 to 16 acre-feet of water per surface acre of pond.
Recirculation systems can reduce water usage to less than 3 acre feet per surface acre of pond.
Authors:
Jimmy L. Avery , Robert P. Romaire and W. Ray McClain
