Metals in Crawfish - Aquaculture and the Environment: A Shared Destiny - page 198

calcium stored by the crawfish in two hard gastroliths on each side of the stomach is
transported to the new shell. The second phase of the hardening occurs as calcium is
absorbed from the water. Once crawfish molt to a reproductively active stage, growth
ceases. A medium size crawfish has a mass of about 25 grams and a head to tail length of 10
centimeters. Mature crawfish can be identified by dark coloration, enlarged claws and
harden sexual structure. Adult males develop prominent hooks on the base of the third and
fourth pair of walking legs. Females will mate several times after molting to the mature
stage.
2.4 Crawfish borrows
Crawfish dig unbranched vertical burrows usually less than one meter deep. The burrows
are used for purposes other than reproduction. The burrows serve as refuge from predators
and provide a moist environment necessary to survive dry periods. Crawfish burrows are
built over several days time by an individual crawfish and the burrow diameter is
dependent on the size of the crawfish. At the bottom of the burrow is chamber slightly
larger than the crawfish. The water level in a burrow is dependent on the moisture
conditions in the surrounding soil. The entrance to a completed burrow is sealed with a
mud plug. Crawfish burrows often have a soil stack or chimney above ground which is
formed by the excavated dirt. Once sealed in the burrow the crawfish is confined to the
burrow until the plug is softened by heavy rainfall or pond flooding.
2.5 Population dynamics
In most forms of aquaculture, known numbers and sizes of juveniles are used to stock the
ponds. Stocking with juveniles is not used in Louisiana crawfish aquaculture. Population
within a pond depends upon reproduction from either stocked or already present mature
crawfish. Density of the population depends upon brood stock survival, successful
reproduction and survival of the offspring. Density can be adversely affected by factors over
which the farmer has no control such as: by low oxygen levels, predators or pesticide
exposure from nearby farming operations. Research has revealed that density greater than
15 crawfish per square yard results in slow growth rates and smaller sized crawfish at
maturity. These factors have made control over population levels one of the most elusive
aspects of crawfish aquaculture.
2.6 Nutrition
Crawfish are omnivores, detritivores (consumers of decomposing organic matter) and most
recently as obligate carnivores because it has been found that they “require” some animal
matter in their diet to optimize growth. A crawfish diet includes living and decomposing
plant matter, seeds, algae, microorganisms, epiphytic organisms, and many invertebrates
such as worms, snails and insects. They will also eat small fish and other smaller crawfish.
Living and decomposing plants are often the most abundant food source in a crawfish pond,
yet contribute very little directly to the nourishment of crawfish. These plants do supply
most of the nutrients in the ecosystem of a crawfish pond. The decomposing plants and its
associated microorganisms (commonly referred to as detritus) are consumed because it has
high food value than living plants. The amount of detritus that can be utilized by crawfish
as the mainstay of their nutrition is limited. This microbe rich detritus is the main food