Grass Carp
Propagation
by
By Kenneth Williams
GRASS CARP, OR
white amur, (Ctenopharyngodon idella), were first brought into the United States
in 1963 by the U.S. Fish and Wildlife Service Warm Water Fish Experiment Station
near Stuttgart, Arkansas. The fish came from Malaysia and were used to study the
potential for weed control in ponds and lakes. Grass carp are one of the largest
members of the minnow family, (Cyprinidae). They may weigh up to 110 pounds but
rarely exceed 35 pounds when stocked in ponds. Their life span is about 12 to 15
years but experience has shown that most ponds must be restocked after 7-8 years
because the fish may be killed, captured by anglers, or die of natural causes.
Also older grass carp do not remove vegetation as efficiently as younger
fish.
Although usually classified as an opportunistic
feeder, grass carp aggressively feed on vegetation. However, grass carp feeding
and growth is greatly reduced when water temperature drops below 57 degrees F.
These fish prefer soft vegetation but consume tougher plant species as preferred
food supplies are diminished. Grass carp readily consume pelleted fish rations
when available. Stocker fingerlings (8-10 inches) can reach a weight of 5-7 lb
in a growing season and 15-20 lb after 3 years provided an adequate food supply
exists.
In natural habitat, adult grass carp are found in
back waters of large river systems in Asia. Aquatic vegetation is abundant and
provides both food supply and cover from predators.
Spawning is determined primarily by photoperiod (day
length) and water temperature. The fish begin to spawn when flood waters swell
rivers, water temperature reaches 70-75 degrees F. and photoperiod is increasing
above eight hours of daylight per day. Mature adults form schools and swim
upstream for many miles into the swift flowing waters found in upper reaches of
the river. The grass carp spawn and release fertilized, semi-buoyant,
non-adhesive eggs down stream. Currents (1-5 feet per second) are required to
prevent eggs from lodging on the bottom, silting over and dying. Eggs moving
down stream are oxygenated and hatch into fry after an incubation period of
24-28 hours. The larvae receive nourishment from the yolk sac for 1-3 days
before active feeding begins. Grass carp fry smaller than 1.25 inches feed on
phytoplankton, zooplankton and invertebrates. As they grow larger aquatic
insects become more important in the diet. Grass carp 2-4 inches long are large
enough to consume multicellular algae and aquatic macrophytes.
Grass carp reach sexual maturity in two-three years
in Oklahoma.
Spawning does not occur in ponds and lakes.
Reproductive organs reach an incomplete state of development and become dormant.
As water temperature rises above 80 degrees F. eggs and milt are resorbed into
the fish.
Natural spawning conditions do not exist for grass
carp in the United States with the possible exception of the Mississippi river.
Successful grass carp spawning and hatching requires a thorough knowledge of the
fish, healthy brood stock, gentle handling and an understanding of induced
hormonal spawning techniques.
Brood Fish Management
Brood fish care begins the summer before they will be
spawned. Grass carp that are in poor condition going into the winter and early
spring make poor spawners. Brood stock should not be of uniform size because the
males are smaller than the females. Brood fish four years old are preferred for
use as induced spawners. Most of these fish will weigh 15-20 lb. Brood fish are
stocked at a rate of 200-1000 lb per acre depending on the number of fry needed.
Males and females are stocked in about equal numbers.
Stock brood fish in a pond containing a large amount
of aquatic vegetation and supplementally feed with a floating, catfish ration at
no more than 1-2 percent of body weight. Sinking pelleted feed should not be fed
because it is not readily accepted by the grass carp. Add additional forages
such as grass clippings or alfalfa if vegetation is eaten before spawning
season.
Maintain good water quality in the pond. Dissolved
oxygen should not drop below 2 mg/L (ppm). Ponds should not be seined if
dissolved oxygen is below 4 mg/L.
Brood fish must be seined carefully to avoid stress
and damage to the fish. Use a knotless mesh seine if possible. Usually 1-2
persons hold up the back of the seine to prevent the fish from jumping over the
net. Protective clothing is advised by some workers to avoid blows from large
grass carp. A baseball catcher's mask can be worn to protect the face. Brood
fish can be seined and placed in round tanks before water temperature reaches
the level required for spawning. This technique allows fish to recover from
harvest stress before spawning is induced. Fish harvested at water temperatures
above 68 degrees F. should be spawned within a day to achieve best results.
Grass carp are ready for induced spawning in late May or early June when water
temperature has reached 70 degrees F. At water temperatures above 80 degrees F.
spawning success declines because resorption of eggs may occur in female
fish.
Sexes are determined by feeling the pectoral fins.
Male grass carp have a rough, sandpaper texture on the pectoral fin and spine,
also protuberances on the head and opercles. The male "pearl organ" should
protrude. Females have a distended abdomen compared to males and a red area
around the egg vent indicating that the fish is ready to spawn. If sex cannot be
determined do not use the fish for spawning purposes.
Induced Spawning
Grass carp can be hormonally induced to spawn in
several ways. Originally, carp pituitary alone was used. This method is still
used, but ovulation success may vary because hormone strength in the carp
pituitary gland is dependent on processing, age and condition of the fish. Carp
pituitary can be used fresh or more conveniently as an acetone-dried extract.
For example, 0.5 g of the extract is ground dry with a mortar and pestle, then
10 cc of sterile water is added, slowly and thoroughly mixed. The mixture is
allowed to stand for about 30 minutes. The hormone dissolves in the water and is
drawn off with a syringe. Settled solids are not used. The preparation is ready
for immediate use or it can be stored in small vials in the freezer. Grass carp
are injected with 3-5 mg of pituitary per lb of female or 0.6- 1.0 cc of the
prepared solution per 10 lb of brood fish. Stress on brood fish must be kept to
a minimum.
Do not remove fish from holding tanks to give
injections. Use a knotless mesh cradle or piece of knotless seine to capture the
fish, hold it to the side of the tank, cover the fish head with a towel to help
prevent movement and inject the hormone intramuscularly with a 20 gauge needle
at the base of the last ray of the dorsal fin. Optimum injection volume for
grass carp is 2 cc or less.
Two injections are used to induce female spawning.
The first injection contains 1/10 of the total dosage. This injection is
followed by the remaining 9/10 of the dosage in 18-24 hours. Male grass carp are
given 1-2 mg per lb of body weight or 0.2-0.4 cc of prepared hormone solution
per 10 lb of brood fish. Male fish are injected at the time the female is
administered the second injection.
Adequate fertilization of spawn requires two males
for each female grass carp. Separate the sexes in separate tanks of water. Use
fin clips or other means to identify individual fish if necessary.
Check female spawning condition beginning one hour
before expected spawn. Handle fish gently! Stress will reduce or prevent
successful or complete ovulation and result in little or no spawn. Spawning
procedures and egg handling should be done in subdued lighting. Direct sunlight
can kill or damage eggs. Carefully capture the female in a large, deep, dip net.
Use an uncoated nylon net or other material that will not damage the fish. Bring
the fish to the side of the tank and lift to the surface of the water. Turn the
fish on her back with the belly exposed slightly above water line. Gently stroke
the belly towards the vent. Copious egg flow indicates the female is ready to
spawn. The female is not ready to spawn if few or no eggs flow freely from the
vent. When a few eggs flow, recheck the fish in 30 minutes. If no eggs are
observed, check the fish again in one hour. Eggs are in an anoxic condition at
ovulation and begin to deteriorate rapidly because they no longer receive a
blood supply from the ovary. Dead or deteriorating eggs look cloudy and should
be removed. Eggs in good condition are usually grayish-green to brown or orange.
Best spawning success occurs when eggs are stripped no later than 30 minutes
after ovulation.
Cover the vent with a thumb or finger when egg flow
indicates the female is ready to spawn. Carefully hold the fish by the caudal
peduncle. Another worker should grab the head of the fish and wrap it in a
towel, making sure to cover the eyes. Dry the fish to prevent water from
dripping into the egg pan. Hold the fish over a clean, dry pan 12 to 18 inches
in diameter and about 6 to 8 inches deep. Raise the head slightly above the tail
and direct the egg flow into the pan.
Females can be anesthetized before egg removal with
MS-222 (1 tablespoon per 10 gallons of water). To anesthetize the fish, place it
in a 100 gallon horse tank filled with water and anesthetizing agent until it is
calm.
Each male is dipped from the holding tank and dried
with a towel. Milt is stripped from the male by starting behind the pelvic fins
and squeezing toward the vent. Milt can be taken prior to actual need and stored
in plastic bags in a refrigerator. Avoid cross contamination. Use one bag per
individual fish. A small amount of water should be added to stored milt
immediately before use. Swirl 5-10 seconds then mix with eggs. Water will kill
sperm in about one minute.
Swirl the eggs and milt gently, with a finger, paint
brush or feather for 2 to 3 minutes. Add a volume of water about equal to the
volume of eggs, stir gently for 3 minutes then pour off as much water as
possible. Repeat water rinse two times to water harden eggs. Eggs become fully
hardened in about 10 minutes. One quart volume contains 225,000 to 250,000
fertilized eggs. Place the eggs in hatching jars.
Water flow should be strong enough to keep the eggs
suspended but not strong enough to wash them out of the hatching jar. Eggs
should hatch after 24 hours incubation in water about 75 degrees.
When larvae hatch they rise to the surface and follow
the current of the overflow. The overflow water can spill over into an aquarium.
The aquarium drain should be screened with 50 mesh per inch net screen. During
the first three days larvae will use food energy stored in their yolk sack.
Larval stocking densities can be as high as 50,000 per gallon of water at this
time. Water flow in the aquarium should remain high enough to suspend larvae
from the bottom of the tank. Stock fry into rearing ponds at three to five days
old
Fill the ponds about a week before fry are to be
stocked to reduce predaceous insects and disease. Wells are the best source of
water for fry ponds. Unwanted fish and insects can be introduced into ponds
filled from streams and reservoirs. Stream or pond water must be
filtered.
Grass carp fry can be stocked into the rearing ponds
at a rate of 100,000 to 500,000 per acre. Fry initially feed on zooplankton. To
produce an adequate supply of these microscopic animals it is usually necessary
to fertilize the pond. Fertilization puts a green "bloom" on the pond caused by
large numbers of phytoplankton or microscopic plants. Zooplankton feed on the
phytoplankton. The amount of fertilizer needed and results of fertilization vary
with physical features of the pond and nutrient loading. Ammonium polyphosphate
has been used successfully at rates of 1-2 gallons per acre foot. Some producers
prefer a mix of organic and inorganic fertilizers. Chicken manure has been used
along with inorganic fertilizer at a rate of 300-400 pounds per acre per week in
0.1-0.5 acre ponds. Research at Langston University has shown that daily
applications of 0.1-0.25 lb ammonium chloride/acre foot provides excellent pond
fertilization.
Begin supplemental feeding with minnow meal as soon
as the fish are stocked. Uneaten meal may fertilize the pond sufficiently to
maintain the desired bloom. Feed fish two to four times daily.
Avoid over feeding fish.
When grass carp have reached a length of three to
four inches they should be removed from high density ponds and restocked into
ponds at a density of 3,000 to 5,000 fish per acre for growth to a stocking size
of eight to ten inches. a survival rate from fry to fingerling of 40%-60% is
considered good.
It is preferable to stock 3-4 inch fingerlings in
growout ponds containing abundant aquatic vegetation. However, the fish should
continue to be supplementally fed with minnow meal until they can take a regular
catfish pellet. A 28%-32%, 3/16 inch, floating catfish pellet can be fed to the
grass carp until they reach harvestable size. Feed no more than 2% of total
standing crop body weight per day, less if other foods are present. Grass carp
production can range from 2,000 to 4,000 pounds per acre in well fed and managed
ponds.
References
Hatchery Manual For Grass Carp And Other Riverine
Cyprinids. R.W. Rottmann and J.V. Shireman. Bulletin 244, University of Florida,
Gainesville, Fl. 32611
Propagation Of Grass Carp. Harry K.Dupree, U.S. Fish
And Wildlife Service, Fish Farming Experimental Station,
Stuttgart, AR 72160
Data is given by:http://www.luresext.edu/aquaculture/grasscarppropogation.htm
|
|
|
|
|
