Metals in Crawfish - Aquaculture and the Environment: A Shared Destiny - page 203

6. Forage management
6.1 Forages
Establishment of a forage-based production system is important in order to produce the
complex ecological community necessary to provide a high quality food source for the
crawfish. The food sources rely on a continuous influx of plant matter that is in turn
consumed by bacteria and other microorganisms. The detritus produced by these
decomposers is the fuel for the food web on which the crawfish rely. The forage crop must
be able to produce adequate portions of plant material on a consistent basis throughout the
growth and harvest seasons. Overproduction of plant material at one time is wasted because
it cannot be stockpiled for later use. Decomposition of large amounts of material in a short
span of time can also lead to oxygen depletion in the water. Too little plant material can lead
to insufficient detritus to support the food web. Selected agronomic crops are the most
effective forage resources for crawfish. These crops are most effective because of their ability
to flourish in the flooded pond environment and their predictable plant material yield.
6.2 Types of forage
Rice is by far the most often used forage plant in Louisiana. Rice is semi-aquatic and grows
well in flooded crawfish ponds. Many varieties of rice have been used as forage. In 2004,
Louisiana State University released the first rice specifically developed for use in crawfish
monocropping. “Ecrevisse” rice exhibits much greater forge biomass production, greater
growth under the extended flood conditions of a crawfish pond and has an improved ability
for post-winter re-growth than the commonly used domestic rice varieties. A sorgam-
sudangrass hybrid that is commonly used by cattlemen for grassing and hay, is a well suited
alternative forage crop for crawfish monocropping systems.
7. Water quality and management
7.1 Overview
Water quality is influenced by both environmental and biological factors. Some
environmental factors such as rainfall and temperature are beyond control. Factors such as
what type of vegetation planted, when planting occurs and how the vegetation is managed
are within the controls of the producer and can affect water quality. Additionally,
maintaining optimum water levels and the timing of flooding ponds can have a positive
effect on water quality.
7.2 Quantity and supply
Surface and subsurface water are both used for flooding in crawfish aquaculture. Surface
water that is pollution-free and free of predatory fish is cheaper than subsurface water but is
usually not reliable as to quality or quantity. Wells provide predator-free water on demand
but require a large investment and reoccurring pumping costs. Pumps are usually powered
by diesel engines. Subsurface water has no oxygen and must be aerated before entering
the pond. Subsurface water must also be monitored for high iron content and hydrogen
sulfide. A pumping capacity of 300 to 400 liters per minute per surface acre is ideal. This
pumping rate is sufficient to exchange all the water in a pond in 4 to 5 days. Flushing a pond