Using Grass Carp in Aquaculture and Private Impoundments

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.

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