In a natural ecosystem, crawfish eat a variety of plants and animals. Crawfish prefer aquatic invertebrates but will feed on detritus and growing vegetation. Detritus, or decomposing organic material, is the base of the complex, self-sustaining food system required in crawfish culture (Fig. 2).
As organic matter decomposes, it becomes coated with bacteria, other microorganisms, and small invertebrates that increase its nutritional quality.
Larger aquatic fauna such as insects, worms, clams, snails and zooplankton feed on the enriched decomposing vegetation. It is these animals that make up the major part of the crawfish diet.
Crawfish eat very little living plant material, but rely on the small invertebrates that live on or near plant stems. Some plant seeds may also be important food resources. Crawfish production can use planted and cultivated forage crops or voluntary natural vegetation.
The forage must provide detritus to the underwater foodweb consistently throughout the growing season. Many aquatic plants, such as alligatorweed (Alternathera philoxeroides), perform this task poorly but can provide substrate and cover for other organisms that are food for crawfish.
Cultivated crops are more consistent from year to year and usually provide for a more consistent supply to the underwater food-web.
Cultivated forages:
Cultivated forages provide a controlled, consistent supply of detritus that results in good crawfish yields. Planting an agronomic crop allows farmers to control the type and amount of available forage.
Forage density is more predictable with an agronomic crop because cultural practices are well established. Research has shown that potential crawfish yield can be increased 2- to 3-fold with good stands of cultivated forage as compared to using natural vegetation only.
Rice (Oryza sativa) is the preferred forage for crawfish. Rice is less detrimental to water quality than terrestrial plants. It can be planted for grain production, with the post-harvest residue and regrowth serving as crawfish forage, or it can be planted solely as a crawfish forage with no intent to produce grain.
When selecting a rice variety for crawfish production consider the culture system (rotational or single cropping), forage biomass production, lodging characteristics, disease resistance, adaptability to local environmental conditions, and rice ratoon potential. Check with your county Extension agent for a list of recommended rice varieties to use solely as planted forages.
Rice for Grain and Forage:
Proper variety selection and cultivation practices will ensure optimum grain yield, but several other considerations are important when crawfish production is to follow. Timing of the grain harvest is determined by the time of planting, the variety, and the weather; it will also affect subsequent forage production. For best results, the ratoon crop should reach maximum forage production after the harvest but should not reach full maturity. Ratoon crops that do reach full maturity wither (senesce) and often become prematurely depleted, causing forage shortages.
Huge amounts of loose plant stalks and leaves remain in the field after grain harvest. This residue should be reduced before the field is re-flooded or it will cause water quality to deteriorate. A straw chopper on the rice combine will chop up the excess straw into smaller pieces that decompose more rapidly during the weeks before re-flooding. Or, the harvest residue can be bailed or burned.
Dead plant material can not be effectively stockpiled in a pond. The only way to increase long term supply is to encourage regrowth of rice stubble after the grain has been harvested. A light application of nitrogen (20 to 40 pounds of nitrogen per acre) can be applied shortly after harvest. The field should then be flushed if adequate moisture is not available. Timely flushing of the field will prevent the loss of nitrogen and encourage rapid stubble regrowth.
Rice for Forage:
It is often desirable to grow a stand of rice as forage only. The variety chosen should produce high vegetative biomass, be resistant to lodging and disease, senesce slowly, and persist throughout the crawfish production season.
Forage rice should be planted early enough to allow maximum vegetative growth without reaching full maturity. Flooding immature rice results in better water quality because there is less decomposing organic matter at the time of fall flooding.
Rice that does not reach full maturity persists longer under flooded conditions and is more likely to generate additional growth in the spring. The potential and requirements for rice production to be adequate for crawfish culture vary from area to area. Follow the recommended practices for your region.
In general, rice is either drilled or broadcast planted in well-tilled seedbeds at rates ranging from 90 to 120 pounds per acre. Although rice requires considerable water for growth, commercial rice producers maintain a shallow flood mainly for weed control and better fertilizer management.
This is not necessary when growing rice for crawfish forage; in fact, standing water on the seed or seedling, if it is too hot, can result in poor stands. Rice may be irrigated during dry periods. Fertilizer usually is required for good rice growth and development; soil should be tested first to determine its fertility.
A common application rate is 60 to 80 pounds per acre of nitrogen (N) and 30 pounds per acre of both phosphorus (P) and potassium (K). Herbicides are not necessary. Some weed invasion is not harmful (and may even be desirable) in crawfish crops. Consult knowledgeable professionals for assistance.
Sorghum-sudangrass:
Good rice stands may be difficult to achieve in some geographical regions and under some environmental conditions, especially during late summer in the southern U.S. Other forage crops, such as sorghumsudan grass hybrid (Sorghum bicolor), may be a good alternative for crawfish forage (Fig. 3).
Sorghum-sudangrass seed is available from most farm suppliers and seed dealers. It grows rapidly, produces larger quantities of vegetative matter than rice, is drought resistant, and may be more reliable than rice for late summer stand establishment.
Sorghum-sudangrass tends to persist longer than rice in flooded crawfish ponds, which makes more forage available during the latter part of the crawfish growing season. Sorghum-sudangrass should be used only in ponds where a forage is planted in late summer. Target planting dates should be early August through early September in the deep South.
If planted too early, sorghumsudan grass is likely to mature before flood-up, which can be detrimental to water quality when plants lodge or large numbers of leaves sluff off into the water. However, planting should not be postponed too long because cooler weather and the shorter days of early fall may inhibit plant establishment and growth. Advanced stands of sorghum-sudangrass should be cut to a 1- to 2-inch stubble in early to mid-August and baled.
Sorghum-sudangrass seed can be drilled or broadcast onto moist soil. Drilling is preferred and is less risky. Seeding rates should be 20 to 25 pounds per acre for drilling and 25 to 30 pounds per acre for broadcasting. Optimum germination temperature is 70 to 85 degrees F. Seeds need adequate soil moisture to germinate, but the seedlings are fairly drought tolerant once they are established.
Sorghum hybrids are sensitive to very low soil pH but seem to tolerate a pH as low as 5.5 without problems. Fertilizers can significantly increase growth and the vegetative biomass of sorghumsudan grass. Follow the Cooperative Extension Service fertilizer and culture recommendations for sorghum-sudan grass in your area. It may be desirable to mow trapping lanes in the pond just before flooding in the fall, especially if sorghum-sudangrass was planted early. Tall plants restrict vision from a boat during early-season harvest.
Authors:
W. Ray McClain , Jimmy L. Avery and Robert P. Romaire
