|Langston University Aquaculture|
Grass Carp Propagation
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.
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.
Hatchery Manual For Grass Carp And Other Riverine Cyprinids. R.W. Rottmann and J.V. Shireman. Bulletin 244, University of Florida, Gainesville, Fl. 32611
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