SRAC Publication No. 3600

VI July 2002 PR

Using Grass Carp in Aquaculture and Private Impoundments

Michael P. Masser*

Grass carp (Ctenopharyngodon idel- might devastate beneficial native grass carp, check with state game la) are native to large river sys- aquatic vegetation in public and fish/natural resource agen- tems of eastern Asia, from the waters prompted many states to cies or Extension fisheries or Amur River on the Russian- ban their further stocking. aquaculture specialists for the Chinese border southward. Although naturalized grass carp legal requirements. Because of their association with do not appear to have established the Amur River, they are some- large, destructive populations, Description times called “White Amur.” they are a controversial topic Grass carp are a member of the among some natural resource Grass carp have been introduced Order Cypriniformes and Family managers. into more than 50 countries for Cyprinidae. Cyprinidae is the foodfish culture and aquatic vege- Table 1 gives the status of grass largest family of freshwater fish tation management. The U.S. Fish carp permitting in the Southern species and includes all the min- and Wildlife Service, in coopera- Region at the time this publication nows and carps. Grass carp have tion with Auburn University, first was written. Before stocking an oblong or elongated body with introduced grass carp into the U.S. in 1963 to investigate their Table 1. Status of permits for grass carp (Ctenopharyngodon idella) stocking usefulness in controlling aquatic in the southern United States. vegetation. No native North American species of fish is as State Status Genetic requirements strictly herbivorous as the grass Alabama legal - no permits required diploids or triploids carp. Therefore, there are no Arkansas legal - no permits required diploids or triploids native species available for aquat- Florida legal - permit required triploids only ic vegetation management. Grass Georgia legal - permit required1 triploids only carp have proven to be effective in controlling many species of algae Kentucky legal - permit required triploids only and submerged aquatic vegeta- Louisiana legal - permit required triploids only tion. Mississippi legal - permit required diploids or triploids Since their introduction, grass North Carolina legal - permit required2 triploids only carp have been stocked into most Oklahoma legal - no permit required diploids or triploids states, either legally or illegally. Puerto Rico legal - dealers permitted1 diploids or triploids Diploid (i.e., normal or non-ster- South Carolina legal - permit required triploids only ile) grass carp have escaped into 1 U.S. river systems and appear to Tennessee legal - dealers permitted triploids only have established reproducing Texas legal - permit required triploids only populations in the Mississippi, Virginia legal - permit required triploids only Missouri and Trinity river Virgin Islands legal diploids or triploids drainages. Fear that grass carp 1Dealers must be permitted, but individuals do not need permits to purchase grass carp from permitted dealers. *Texas Cooperative Extension, The Texas 2Permits are required only for ponds larger than 10 acres or with more than 150 fish. A&M University System relatively large scales; the head is and sperm, and incubation of the that grass carp consume literally broad and the belly rounded eggs. Triploid grass carp are fur- hundreds of aquatic plant species. (Fig.1). The dorsal and anal fins ther manipulated by shocking the It is probably safe to say that if are short with no spines and the eggs to produce the triploid steril- they are hungry and deprived of caudal fin is deeply forked. Their ity. After fish reach 4 to 12 inches, preferred vegetation, they will jaws have simple lips with no blood cells from each fish are test- consume any plant material they teeth and they have no barbels ed using a Coulter Counter™ to can find, including terrestrial (i.e., whiskers). Like other verify the triploid chromosome plants overhanging the water. Cyprinidae, grass carp have pha- number. This increased handling Young grass carp (less than 3 ryngeal teeth (i.e., in the throat). and testing is the reason triploid pounds) prefer soft vegetation These pharyngeal teeth are in two fish usually cost two or three and consume species such as rows and enable the grass carp to times as much as diploids. duckweeds, filamentous algae and cut/shred the vegetation it con- chara. Any preference for fila- sumes. Their flesh is white, firm Life history and plants mentous algae appears to and not oily, but the muscle mass controlled decrease with age. The most pre- contains “Y” bones. Grass carp ferred plants are succulent and flesh is considered a delicacy by Grass carp spawn naturally only low-fiber. As carp grow, more many seafood enthusiasts. in rivers with high water flows plant species and less succulent and appropriate temperature. The ones are added to the diet. Table 2 water/current velocity must be illustrates preference rates based sufficient to keep the semi-buoy- on research carried out in tank ant eggs suspended as they are studies of mostly juvenile grass carried downstream. If the eggs carp. It should be emphasized fall to the bottom, they will suc- that even though grass carp will cumb to siltation and low dis- eat a particular plant they may solved oxygen. It is estimated that not control that plant unless fish the eggs must remain suspended are stocked in sufficient numbers for 20 to 40 hours, which means and preferable plants are not that they may travel 30 to 110 available. It is not desirable for miles (50 to 180 km), depending grass carp to completely remove on water velocity, before hatching. all rooted vegetation because this Therefore, grass carp cannot may increase the turbidity associ- spawn in ponds. Figure 1. A grass carp. ated with intense algal blooms. Fry and early juvenile grass carp Grass carp are fed commercial are stocked into fertilized ponds pelleted diets as juveniles in where they initially feed on plank- Diploid versus triploid hatcheries, and they never seem to ton and benthic invertebrates. At 1 forget this. They will continue to Normal grass carp have 48 chro- inch in length, grass carp start consume pelleted diets through- mosomes. This is known as the feeding on macrophytes (non- out their lives. Pond owners often diploid or 2N chromosome num- microscopic plants) but can and complain that grass carp consume ber. Sterile grass carp are pro- do consume some animal foods fish food rather than the plants duced in hatcheries by physically throughout their lives. they were intended to control. shocking the eggs immediately Fingerling grass carp will con- Grass carp grow rapidly under after fertilization either with tem- sume insect larvae, other inverte- favorable conditions. Food con- perature (hot or cold) or pressure. brates, and even small numbers of sumption rates are influenced by The resulting fish are triploids fish fry, but only when desirable temperature, age and size of fish, (3N) because each cell has an vegetation is unavailable. Several dissolved oxygen and plant extra set of chromosomes. researchers suggest that the small species. Grass carp consume vege- Triploids are infertile. amount of animal matter they tation intermittently at tempera- There appears to be no difference consume probably is the result of tures as low as 37 oF (3 oC). They in vegetation preference between ingesting epiphytic organisms eat steadily at 50 to 60 oF (10 to diploid and triploid grass carp. associated with plants. 16 oC), with optimal consumption However, triploids consume only Research has shown that the size at temperatures between 70 and 90 percent of the amount diploids and type of vegetation are the fac- 86 oF (21 and 30 oC). consume. Triploid grass carp also tors that influence consumption Consumption rates at optimal do not live as long as the diploids rates the most. (Most of this temperatures vary with fish size. (10 to12 years versus 20+ years, research has been conducted on The reason grass carp are so good respectively). All grass carp sold fingerlings and juveniles and not at controlling aquatic vegetation is in the U.S. are from private hatch- on adult fish.) Generally, grass that they have a very short gut eries and have been artificially carp prefer the soft, tender tips of compared to other herbivores. spawned using hormone injec- young, growing plants and sub- This short gut decreases retention tions, manual stripping of eggs merged vegetation. It is known time (less than 8 hours) in the gut and reduces digestive efficiency to sume 6 to10 percent of their body peratures are cool and grass carp only 60 or 70 percent. Because of weight in vegetation each day consumption is correspondingly this reduced efficiency, they eat (wet weight basis). As fish grow, low. Some species of algae, such more vegetation. the consumption rate increases. as Pithophora, are particularly Research has shown that juveniles Fish weighing 2 to 2.5 pounds (1 unpalatable. In one 5-acre catfish (2.4 to 6 inches, 6 to 15 cm) con- to 1.2 kg) can consume more than fingerling pond choked with their body weight each day (in Pithophora, 200 3- to 5-inch grass some cases 300 percent). Larger carp per acre (1,000 total) were Table 2. Common aquatic plants fish can consume up to their body required to control the problem. consumed by grass carp. weight per day under ideal condi- In 2 weeks the producer was able Plant Order of tions. Reportedly, fish larger than to seine and remove the catfish 10 pounds eat only 20 to 30 per- and recover the grass carp, which common name preference1 cent of their body weight. had grown to 8 inches. Obviously hydrilla 1 Obviously, at these consumption this was an extreme case, but it chara (muskgrass) 2 rates grass carp can quickly illustrates how water temperature pondweeds reduce vegetation if stocked in and vegetation preference must be (Potamogetan)3 proper numbers, in good quality taken into consideration. bushy pondweed water, and at optimum tempera- Table 3 gives stocking rate recom- (Southern naiad) 4 ture. mendations. It is best to stock elodea 5 The water quality needs of grass grass carp during cool weather, as watermeal 6 carp are similar to those of most they do not handle well at tem- o o duckweeds 7 other warmwater fish. Consump- peratures above 75 F (24 C). tion is best at dissolved oxygen Often managers stock too few water-fern concentrations higher than 4 (Azolla)7 fish to control the problem. If mg/L (ppm); consumption coontail 8 grass carp are over-stocked they appears to stop at dissolved oxy- simply have little to eat and do hygrophila 9 gen concentrations below 3 mg/L. not grow. They will then consume cattail2 10 Grass carp can tolerate moderate pelleted feed if it is available. It is torpedograss 10 salinity but eat less as salinity usually better to overstock than to increases from 1.3 to 9 parts per salvinia 10 understock. thousand (ppt). They stop eating water-aloe if salinity reaches 12 ppt. While grass carp live many years, (Stratiotes)11Prolonged exposure to 9 to 10 ppt their effectiveness for vegetation watercress 12 salinity is lethal, but they can sur- control decreases significantly torpedograss 13 vive for short periods at even after 5 to 7 years. At this age their growth rate and food consump- Eurasian watermilfoil 14 higher salinity. tion slow. Ponds usually need to eel grass (Vallisneria)15 Stocking rates be restocked with grass carp maidencane2 every 5 to 7 years; or, each year 20 (Panicum)16Stocking rates should be based on percent of the original number parrot feather 16 grass carp vegetation preferences can be restocked to offset mortal- know grass and the biomass of plants in a ity (especially with triploids). (Paspalum)17pond. Many submerged plants In new or renovated ponds, three water hyacinth 17 can have a very high biomass, to five grass carp per surface acre partly because they are 90 to 95 giant bulrush2 18 can be stocked to prevent sub- percent water. Species such as merged aquatic vegetation from water lettuce 18 hydrilla, southern naiad, chara, becoming established. This usual- soft-stem bulrush2 19 elodea and coontail can have a ly prevents submerged aquatic water lilies 19 total wet biomass of more than 10 weeds for 5 to 7 years. tons per acre. 1Adapted from “Grass Carp - A Fish for Biological Management of Hydrilla and Filamentous algae are often a Preventing escape Other Aquatic Weeds in Florida” by David problem in fry and fingerling L. Sutton and Vernon V. Vandiver, Jr., ponds, making it difficult or Because grass carp are natural University of Florida IFAS, Bulletin 867; impossible to harvest the fish. inhabitants of rivers, they readily and from “Managing Aquatic Vegetation This is particularly true in the escape ponds that overflow. A With Grass Carp - A Guide For Water spring of the year. Larger num- flow of only a couple of inches Resource Managers” edited by John R. will allow even large grass carp to Cassani, American Fisheries Society, bers of small grass carp are need- ed to control filamentous algae escape. Therefore, many states Bethesda, Maryland. Some plants have recommend, or even mandate, the same number, which means grass than many other plant species carp like them equally. because filamentous algae is not a that barriers be placed across emergency spillways (i.e. canals, 2Young, succulent, underwater shoots are favored food and it develops in the late winter when water tem- culverts, etc.) before grass carp preferred. can be stocked into ponds. Table 3. Suggested stocking rates (per acre) for grass carp in private infused with rotenone called Prentox‚ Prenfish™. See the label ponds.1 for information about the training Percent of pond infested by noxious vegetation required to use this product. 0 - 10 10 - 30 30 - 50 > 50 Conclusion Stocking density2 5 10 - 12 12 - 15 20 or more 1Grass carp must be large enough to avoid predation by other species of fish. If there are Grass carp can effectively control predatory species (e.g., largemouth bass) in the pond, grass carp should be larger than 8 aquatic vegetation, particularly inches. submerged vegetation. The key to using grass carp is to stock the 2If the vegetation to be controlled is low on the grass carp’s preference list, increase stocking by 30 to 50 percent. Some states specify stocking numbers on their permits. proper number based on their vegetation preferences, the water temperature, and the biomass and Many different materials and Removal methods pond coverage of the plants. designs can be used for escape- Grass carp are especially advanta- ment barriers. Probably the best It is very difficult to seine grass geous in aquaculture because design uses horizontal bars carp because they can jump so they: 1) eliminate chemical treat- spaced 2 inches (5 cm) apart (Fig. well. They are easiest to remove ments that could involve water 2). Leaves and small branches can when ponds are drained. Other use restrictions; 2) are relatively pass through the barrier without methods of removing them inexpensive; and 3) usually do not clogging it. Net or mesh type bar- include angling, bow-fishing and have to be handled. riers trap leaves and branches and using rotenone baits. Grass carp can then collapse under the can occasionally be caught using Selected references: increased water pressure. Escape- heavy-duty fishing tackle and a dough-type bait (like that used for Cassani, J.R., editor. 1996. Managing ment barriers should be at least a Aquatic Vegetation With Grass Carp, A foot above the highest expected common carp). Grass carp have a Guide for Water Resource Managers. water level to keep grass carp habit of staying near the surface American Fisheries Society: Bethesda, from jumping over them. Grass and this makes it relatively simple Maryland. carp are very adept at jumping. to use a bow. Grass carp are sus- Shireman, J.V. and C.R. Smith. 1983. ceptible to rotenone (a restricted- Synopsis of Biological Data on the use pesticide that requires an Grass Carp Ctenopharyngodon idella applicators license). Prentiss, Inc. (Cuvier and Valenciennnes, 1844). FAO Fisheries Synopsis No. 135. Rome. has developed a pelleted bait Sutton, D.L. and V.V. Vandiver, Jr. 1998. Grass Carp, A Fish for Biological Management of Hydrilla and Other Aquatic Weeds in Florida.

4-INCH TREATED OR 2-INCH STEEL POST

3/4- INCH 2 INCHES 48 INCHES ROUND BAR BETWEEN BARS

3 1 /8 - T O /2- 20 FEET 1/4 X 2 X 4 - INCH ROUND INCH FLAT BAR Figure 2. Example of a spillway barrier.

SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software Steering Committee. Fact sheets are revised as new knowledge becomes available. Fact sheets that have not been revised are considered to reflect the current state of knowledge.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 00-38500-8992 from the United States Department of Agriculture, Cooperative State Research, Education, and Extension Service.