Crayfish Information
General Information
Crayfish, also called crawfish or crawdad, are closely related
to the lobster. More than half of the more than 500 species occur
in North America, particularly Kentucky (Mammoth Cave) and Louisiana
in the Mississippi basin. Crayfish also live in Europe, New Zealand,
East Asia and throughout the world, including the Tristan da Cunha
Islands. Nearly all live in freshwater, although a few survive in
salt water. Crayfish are characterised by a joined head and thorax,
or midsection, and a segmented body, which is sandy yellow, green,
or dark brown in colour. The head has a sharp snout, and the eyes
are on movable stalks. Crayfish are usually about 7.5 cm (3 inches)
long.
The crayfish is typical of most shrimplike crustaceans and is characterised
by a joined head and thorax, or midsection, and a segmented body,
which is sandy yellow, green, white, pink or dark brown in colour.
Crayfish are usually about 7.5 cm (3 inches) long. Among the smallest
is the 2.5-centimetre-long Cambarellus diminutus of the south-eastern
United States. Among the largest is Astacopsis gouldi of Tasmania;
its length may reach 40 cm and its weight about 3.5 kg (8 pounds).
The head has two pairs of sensory antennae and a pair of eyes on
movable stalks. The appendages, or pereiopods, of the thorax include
four pairs of walking legs which, as well as walking, are to probe
cracks and crevices between rocks looking for food. Crayfish also
own one pair of clawbearing chelipeds, which it extends in front
of its body while moving. These strong pinchers are specialised
for cutting, capturing food, attack, and defence. A pinch can hurt!
The crayfish also has several pairs of specialised food handling
‘legs,’ bailers to cycle water over the gills, and five
pairs of swimmerets which are under the abdomen. All of these ‘legs’
can be regenerated if broken off.
Crayfish have a hard outside skeleton. This jointed exoskeleton
provides protection and allows movement, but limits growth. As a
result, the crayfish regularly gets too big for its skeleton, sheds
it, and grows a new larger one. This is called molting. and occurs
six to ten times during the first year of rapid growth, but less
often during the second year. For a few days following each molt,
crayfish have soft exoskeletons and are more vulnerable to predators.
Crayfish, common in streams and lakes, often conceal themselves
under rocks or logs. They are most active at night, when they feed
largely on snails, algae, insect larvae, worms, and tadpoles; some
eat vegetation (various water plants). A dead fish worms, corn,
and salmon eggs are also favourites of the crayfish. Studies show
that adults (one year old) become most active at dusk and continue
heavy feeding activity until daybreak. Young crayfish are more likely
to be the ones out during bright sunny days, while the older crayfish
are more active on cloudy days and during the night. General movement
is always a slow walk, but if startled, crayfish use rapid flips
of their tail to swim backwards and escape danger.
Most crayfish live short lives, usually less than two years. Therefore,
rapid, high-volume reproduction is important for the continuation
of the species. Many crayfish become sexually mature and mate in
the October or November after they're born, but fertilisation and
egg laying usually occur the following spring. The fertilised eggs
are attached to the female' swimmerets on the underside of her jointed
abdomen. There the 10 to 800 eggs change from dark to translucent
as they develop. The egg-carrying female is said to be ‘in
berry,’ because the egg mass looks something like a berry.
Females are often seen "in berry" during May or June.
The eggs hatch in 2 to 20 weeks, depending on water temperature.
The newly-hatched crayfish stay attached to their mother until shortly
after their second molt.
The natural predators of the Crayfish include alligators, burbots
(a type of cod), chicken turtle, painted turtle, desman (a type
of otter), grackle (a type of a bird).
In the open circulatory system blood flows from the heart through
the arteries and returns into open sinuses. The digestive system
has a stomach for grinding food and a gland for chemical processing.
The antennal gland is the main excretory organ.
Crayfish are part of the order Decapoda constituting the families
Astacidae (Northern Hemisphere), Parastacidae, or Austroastracidae
(Southern Hemisphere). The most common genera of North America include
Procambarus, Orconectes, Faxonella, Cambarus, Cambarellus, and Pacifastacus.
Austropotamobius is the most common genus of Europe. The genus Astacus
occurs in Europe, the genus Cambaroides in East Asia. The arthopod
class also includes centipedes, crustaceans, insects, millipedes,
mites, scorpions and spiders.
The importance of the crayfish in a game fish's diet can be played
up or down depending on one's point of view. Down: Studies show
that trout eat more aquatic insects than any other item. Up: Biological
studies also show that stream-living trout will select the largest
prey items that they can swallow. When crayfish are available, they
will be eaten!
Regardless of your perspective, crayfish can't be overlooked because
of their size and nutritional value. Can you imagine how many ants
or mayflies a trout would have to eat to equal the food value gained
from one average-sized crayfish? Then factor in how much energy
the fish would have to expend to feed on those hundreds of tiny
insects. The same principle would hold true for bass.
My sporadic (I usually release my catch) inspection of trout stomach
contents frequently turns up crayfish. I found crayfish, usually
in several pieces, in trout as small as 7.5 inches. Several times
I removed parts of more than one crayfish from a single stomach.
Although anglers seemingly in-the-know favor the "just molted"
soft-shelled "crabs" for bait, all of the consumed crayfish
that I examined were "hard-shells."
The Fishing Connection
What does all of this tell the serious angler? Crayfish are eaten
by trout and bass. Fish can't afford to pass up such a large meal.
They do make an effective bait. Crayfish to be used for bait are
easily collected with a small minnow net. Small rocky streams are
a good place to check. Numbers vary from stream to stream, so keep
looking until you locate a hotspot. Softshells are good, but normal
crayfish probably will do just as well. Collect assorted sizes.
I have had much success on trout with Rebel's Teeny Wee Crawfish,
a 1.5-inch long crayfish-like crankbait. Of the dozens of trout
that this lure has produced for me, several have been browns of
over 16 inches. What really surprised me, however, were some of
the smaller trout that I landed trout from 7.5 inches all the way
down to tiny browns and rainbows of only 5 inches.
Because species and crayfish colors vary, it's best to fish with
a bait or lure that matches the natural. Fish them in shallow, rocky
places, for crayfish favor these areas. Rig naturals so they can
be retrieved backwards, the way that crayfish always swim. Fishing
at dawn, dusk, or during the night would best imitate natural movement.
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