Aquatic weeds and their utilization 333Crayfish
Crayfish or freshwater lobsters are an under-exploited food source. They are
produced commercially in some European countries, a few areas of U.S.A., and
a few tribes in New Guinea use them extensively as their major protein source.
Boiled in salt water, they are a delicacy and a gourmet's delight.
There are over 300 known species and a few are exclusively herbivorous.
Such varieties appear promising for aquatic weed control and utilization.
Orconectes causeyi, a species native to the western U.S.A., has been used
experimentally for weed control and was effective against pondweeds.
Orconectes nais has been shown to control aquatic weeds in Kansas, U.S.A.
Beyond that little is known about weed control by the herbivorous species of
crayfish (NAS 1976). In general, crayfish is thought of more in terms of an
available crop associated with aquatic weeds, not as a weed-control agent. Red
crayfish(Procambarus clarkii) is widely farmed in California and Louisiana in
flooded rice fields and lives mainly on aquatic weeds that grow among the rice.
The crayfish is too small to eat the rice seedlings at planting, and by the time the
crayfish mature, the rice plants are too tall and fibrous to be eaten.
Before crayfish are introduced into new areas, their effect on rice production
should be studied carefully. Imported crayfish have become a problem in Japan
and in Hawaii where rice paddy dikes have been weakened by their burrowing.
Some species of crayfish eat tender shoots of newly germinated rice and should
be avoided.
7.6.2 Livestock fodder
Aquatic weeds can be used as feed for livestock after suitable processing.
Excessive moisture content in fresh plants restricts the ability of animals to
obtain adequate nourishment. The palatability of feed processed from aquatic
weeds compares poorly with that of most other conventional feeds. A good feed
must contain adequate levels of protein, fat, carbohydrate, vitamins, and mineral
nutrients for satisfactory growth. The feed should have fairly low fiber content
so that most of the organic matter is highly digestible even to non-ruminant
animals.
The proximate compositions of some aquatic weeds which appear suitable as
feed are compared with that of alfafa hay, as given in Table 7.4. As can be seen,
the composition of dried samples of many species show that they were inferior
to alfafa hay for use as livestock feed, but some species were as suitable, or
better, than dried alfafa. On average, aquatic weeds contained less crude protein,
somewhat more ash and fat and slightly less cellulosic fiber than alfafa.
Submerged and floating plants usually have higher values for crude protein and