Fall Flooding of Crawfish Ponds

Van Pennington
Area Extension Agent

Proper and correctly timed fall flooding of crawfish ponds is a major factor influencing  total yield .  Flooding too early often results in oxygen and other water quality problems.  Late flooding can result in low survival and a late crop.

In late summer there are females in burrows laying eggs and hatching young.  The number of eggs being laid by each female may vary from less than 200 to over 700, depending on her weight, maturity and condition.

Red Swamp females generally produce more eggs than White River.  Red Swamp eggs hatch in two to three weeks.  Eggs of White River females usually take slightly longer to hatch.

Once hatched, the young stay attached to the female for approximately one week.  At this time they release, become free swimmers, and begin to forage for themselves.

Determining the Time to Flood

When young crawfish are present in a majority of the burrows, it is time to flood.  This can be determined by dipping out burrows with a small mesh dip net or by siphoning water from the burrow with plastic tubing.  Newly hatched young will eventually die if water is not provided.  Ponds should be flooded as early as possible to take advantage of the warm weather.  This water control helps assure an early crop, ready to harvest when prices are higher.

Watch air temperatures in early fall to determine when to check burrows.   Daytime temperatures averaging 80°F and nighttime 60°F should occur in Arkansas around October 1.

Recruitment

Flooded ponds usually contain several groups, or age classes, or crawfish.   These age classes include holdover from the preceding season, and young-of-the-year.

Young-of-the-year comprise at least three age classes.  The first age class of young-of-the-year enters the pond when it is flooded.  Two other dominant age classes of young-of-the-year hatch in the pond later.  Spawning does not take place at one time, so there are several of these young-of-the-year.  The appearance of these young-of-the-year crawfish is called recruitment.

The number of age classes, numbers within age classes, survival rate, food availability and water quality will determine overall pond yield.

Survival

With good management, at least 50 percent of each young-of-the-year age class should survive to a harvestable size.  Death losses increase from causes such as predators, stress, poor water quality, climate conditions and harvesting.

Predation by fish or poor water quality can virtually destroy all crawfish in a pond.  Fish can and must be controlled by summer draining and of a toxicant.

An adequate supply of high quality water is one of the most important factors in successful crawfish production.  Aeration combined with recirculation or flushing with water of high oxygen is critical to survival.  The dissolved oxygen content should be a minimum of 3 ppm at all times.  For intensive crawfish culture, the water should be recirculated at least two times a week during the fall and in the warmer months when oxygen levels are low.

During the year, survival of an age class is usually less than ten percent after intensive harvesting.  The survival rate is adequate to serve as brood stock.

Stunting

The principal causes of stunting include overcrowding, lack of food, poor water quality and insufficient trapping.

The growth rate depends largely on the food available, water temperature and how crowded the pond is.  Approximately 11 molts are required to reach full maturity.  A molt usually occurs every 6 to 18 days.   In a well-managed pond a crawfish may grow 1/2 inch per molt.  With optimum temperatures of 70° to 80°, maturity, or 3 1/2 to 5 inches in size, may be reached in 60 to 90 days.  With lower temperatures or shortage of food, this period may exceed 150 days.

Crawfish may reach maturity and stop growing at sizes smaller than 3 inches.  When a high percentage of the population is comprised of these small inferior males, it will probably affect the next year's young.

The best way to prevent this stunting is to intensively harvest when harvestable size is reached.

One way to determine if stunting is occurring is by checking males for "Form 1" condition.  This is characterized by the presence of prominent hooks at the base of the third and fourth walking legs and enlarged claws.

Another sign of impending stunting is the extensive growth of "crud" on shells.  Such crawfish are not growing fast and usually have a dull off color.

Toward the end of the season, stunting may occur because the food supply is depleted.  In this case, hay or straw should be added to the pond to provide forage for the crawfish to eat.

Pond Monitoring

It is very important to know how crawfish are progressing in a pond.   They cannot be observed like row crops.  They must be retrieved from the pond with dip nets or traps.  Small crawfish should be sampled with a small mesh dip net.   Larger crawfish become difficult to catch and may require a small mesh trap.

Walk the edge of the entire pond and make a dip every 15 to 20 paces.   Extend the net away from the bank and rake quickly back toward the bank, making sure to keep the net frame against the bottom.

Make sure a representative sample is obtained.  A minimum of 50 young should be caught with a dip net and at least 100 with a trap.  The young should be measured and age classes determined and grouped each time the pond is monitored.  All data should be recorded for comparison during the season.  Sampling should be done several times during the fall.

Interpretation of Sampling

If sampling results in very few small crawfish (less than one per dip) throughout fall, yield will probably be poor.  The presence of three age classes and sustained catch of over one crawfish per dip indicate average yield, while an average of over two crawfish per dip indicates good yield.  Average size increasing throughout the fall and presence of multi-age classes indicate they are growing and survival is good.   Abundant young-of-the-year should be evident by mid-November.

A consistent catch of three or more small crawfish per dip during the fall may indicate overcrowding.

Mr. Pennington is located in the Desha County Extension Office.

FSA9002-3M-2-85