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Figure 19. Grass Carp, SIUC 23044, 289 millimeter SL, from Alexander County, Illinois.
The Grass Carp (fig. 19) is a large species, often reaching over 1 m TL. Maximum size is about 1.5 m TL and 45 kg or more (Robison and Buchanan, 1988; Etnier and Starnes, 1993; Laird and Page, 1996). The species has an oblong body, wide head, and rounded belly. The dorsal fin has i-iii (7-8) rays. The anal fin is set far to the rear on the body and has ii-iii (8-10) rays. The origin of the dorsal fin is anterior to the pelvic-fin base. Both dorsal and anal fins are rounded. The caudal fin is deeply forked. All fins are soft-rayed. The lateral line is complete, with 34-45 scales, and is slightly decurved. The mouth is terminal, somewhat oblique, and lacks barbels. The eyes are at the approximate level of the axis of the body or slightly higher. The gill rakers are short, unfused, widely set, and number 12-16 on the first arch. The pharyngeal teeth have deep groves, are in two rows, and may count 2,5-4,2; 2,4-4,2; or 2,4-5,2 (fig. 20; Shireman and Smith, 1983). Scales along the dorsum and sides are usually dark-edged, giving a cross-hatched effect. Juvenile Grass Carp are silvery (fig. 21). Adults are often dark gray along the dorsal surface and brassy along the sides of the body (fig. 22). In some situations, the species may appear much darker and olivaceous on the dorsal surface (fig. 23). The fins are typically green-gray to dull silver. Grass Carp meristics are given in appendix B.
Figure 20. Pharyngeal teeth (2,4-5,2) of Grass Carp,
Figure 23. Adult Grass Carp, 455 millimeter SL, from Reelfoot Lake,
Although both sexes may develop breeding tubercles, they typically appear only on males. Breeding tubercles may occur along the upper surface of the pectoral fins, the ridges of the pectoral-fin rays, on the first dorsal-fin ray, and over the dorsal surface of the caudal peduncle (Opuszynski and Shireman, 1995).
The Grass Carp can be distinguished from native cyprinids by the position of its anal fin, which is set far back on the body (fig. 19) and the deep lateral grooves in its pharyngeal teeth (fig. 20). Native cyprinids have an anal fin that is more anterior than that of the Grass Carp, and have pharyngeal teeth that lack deep lateral grooves. The Grass Carp closely resembles Black Carp, but can be distinguished by its pharyngeal teeth and (in most cases) body color. The Grass Carp has long, serrated pharyngeal teeth (sometimes with hooks) whereas those of adult Black Carp are smooth and molariform. Adult Grass Carp are lighter in color than Black Carp, especially the fins. For additional characteristics useful in distinguishing Black Carp from Grass Carp, refer to the Black Carp species account.
Concern over ecological impacts in natural systems has resulted in widespread use of triploid Grass Carp that are presumably sterile (Clugston and Shireman, 1987). Morphologically, triploids are indistinguishable from (fertile) diploids (Bonar and others, 1988). Triploid Grass Carp may be produced using heat, pressure, or chemical shocking of the fertilized eggs (Clugston and Shireman, 1987; Opuszynski and Shireman, 1995). However, because most treatments used to create triploid Grass Carp are not 100 percent effective, the ploidy of each fish must be verified (that is, either diploid, 2n or triploid, 3n). Ploidy is typically determined by analysis of blood taken from live or freshly killed specimens. The preferred technique uses a particle sizer (for example, Coulter Counter) with a channelyzer to estimate ploidy by analyzing the distribution of red blood cell nuclear volumes (Wattendorf, 1986).
Before widespread use of triploid Grass Carp became the main alternative to releasing reproductively viable (diploid) individuals, there was limited production and release of a sterile hybrid formed by crossing female Grass Carp with male Bighead Carp (Fuller and others, 1999; Nico, 2005). The resulting offspring of this cross had closely spaced gill rakers and an abdominal keel like the paternal Bighead Carp, as well as pharyngeal teeth and an elongated body resembling the maternal Grass Carp (Berry and Low, 1970; Verigin and others, 1975; Kilambi and Zdinak, 1981). Although hybrids can allegedly feed on either plankton or macrophytes, Kilambi and Zdinak (1982) reported a preference for zooplankton. Karyology of the hybrid was given in Marian and Krasznai (1978) and Beck and others (1980). Kilambi and Zdinak (1981) described the hybrid larvae. Meristics for Grass Carp X Bighead hybrids are given in appendix B.
Grass Carp have been artificially hybridized with Common Carp (Makeyeva and Verigin, 1974a; Stanley and Jones, 1976; Avault and Merowsky, 1978), Bighead Carp (Andriasheva, 1968; Beck and others, 1980), Silver Carp (Andriasheva, 1968) and Black Carp (Makeyeva and Verigin, 1993).
Sexual maturity is reached at an average age of 2-5 years in subtropical/tropical areas and 4-7 years in temperate regions (Alikunhi and Sukumaran, 1964; Bardach and others, 1972). Males generally mature a year earlier than females (Opuszynski and Shireman, 1995). Shireman and Smith (1983) reported that Grass Carp may mature earlier than these averages. For example, mature 1-year old males and 2-year old females were documented in tropical India and Malaysia (Hickling, 1967). Alternately, maturation can take 9-10 years in cold climates (Makeeva, 1963, in Hickling, 1967). The condition of gonads through the stages of development was reviewed by Opuszynski and Shireman (1995). Fecundity has been found to range widely, from 255,000-2,000,000 eggs (Vinogradov and others, 1966; Gorbach, 1972; Shireman and Smith, 1983; Opuszynski and Shireman, 1995), and fecundity reportedly increased with age and mass (Gorbach, 1972). Egg and larval development were described by Bailey and Boyd (1970) and Nakamura (1969). Although Grass Carp spawning commonly occurs in large rivers, Tang (1960a,b) reported an unusual instance of a few spawning events in a Taiwan reservoir. The success of those particular spawning events is uncertain (Nico and others, 2005). Krykhtin and Gorbach (1981), who studied the downstream drift of Grass Carp eggs in the Amur Basin, determined that spawning occurred at water temperatures between 17- 26 °C, with peak activity at 21-26 °C. Stanley and others (1978) reviewed literature from Asia and Europe on requirements for spawning, including temperature, water level fluctuation, and spawning site characteristics.
The Grass Carp is a large species that can attain a weight of 45 kg (Robison and Buchanan, 1988; Etnier and Starnes, 1993) and a length of 1.5 m TL (Laird and Page, 1996). Typical longevity is about 5-11 years (Berg, 1964), but an individual in the Amur River was estimated to be 21 years, based on scale growth rings (Gorbach, 1961). Growth is relatively rapid, especially in the tropics where it can average 10 g per day (Hickling, 1967).
Typical habitat includes quiet waters, such as lakes, ponds, pools, and backwaters of large rivers, and individuals generally do not travel long distances except for the annual spawning migration (Mitzner, 1978; Nixon and Miller, 1978; Bain and others, 1990). Nevertheless, there are reports of juvenile Grass Carp traveling as far as 1,000 km from their original spawning grounds (Stanley and others, 1978). Shallow water is the generally preferred habitat, although deeper waters are used when temperatures decrease (Nixon and Miller, 1978). A number of experimental studies have reported environmental tolerances for Grass Carp. Fry and fingerlings have been reported to tolerate water temperatures from 0-40 °C (Stevenson, 1965; Vovk, 1979), and Stevenson (1965) reported that fingerlings in small ponds in Arkansas survived 5 months under heavy ice cover. Chilton and Muoneke (1992) reported an upper lethal temperature range for fry as 33-41 °C, and for yearlings as 35-36 °C. Bettoli and others (1985) documented a thermal maximum of 39.3 °C and a preferred temperature of 25.3 °C. Collee and others (1978) reported that feeding declined sharply below 14 °C. Nico and others (2005) reviewed temperature tolerance of Grass Carp and the other Chinese carps.
Oxygen consumption (per gram of body mass) increases with higher water temperature and decreases with fish age and mass (Chen and Shih, 1955; Wozniewski and Opuszynski, 1988). The lethal low oxygen level for juveniles was <0.5 mg/L (Negonovskaya and Rudenko, 1974). The maximum pH for culture of Grass Carp was reported as 9.24 (Liang and Wang, 1993). Egg hatching was delayed below pH 6.5 and increased mortality and deformation of larvae occurred below pH 6.0 (Li and Zhang, 1992). Sensitivity to low pH decreased with age (Li and Zhang, 1992). Median lethal concentration of ammonia was determined to be 1.05 mg/L (Gulyas and Fleit, 1990).
The Grass Carp appears to be tolerant of low levels of salinity, and may occasionally enter brackish-water areas. Fry (32-50 mm TL) survived transfer from freshwater to a salinity of 12 ppt (Chervinski, 1977). Adults (2+ years) survived 10.5 ppt salinity for about 24 days and 17.5 ppt for 5 hours (Cross, 1970). However, Grass Carp acclimated to 3, 5, and 7 ppt had an upper tolerance of about 14 ppt (Kilambi and Zdinak, 1980). Maceina and Shireman (1980) showed that fingerlings reduce feeding at 9 ppt and stop feeding altogether at 12 ppt; thus, they predicted Grass Carp could inhabit brackish water bodies up to 9 ppt. Maceina and Shireman (1979) reported that the species can tolerate 14 ppt for as long as 4 days, but that the upper long-term tolerance of fingerlings to saline waters was lower, about 10-14 ppt. Maceina and others (1980) noted that oxygen consumption decreased along a salinity gradient of 0-9 ppt. Movement of Grass Carp from one river to another through a brackish-water estuary (Pavlov and Nelovkin, 1963, in Cross, 1970) is not surprising given the species’ tolerance to low levels of salinity. Avault and Merowsky (1978) reported food preference and salinity tolerance of hybrid Common Carp X Grass Carp.
The species is probably best known for its ravenous appetite for plant matter (especially macrophytes); however, small Grass Carp feed on invertebrates before switching to plants. Watkins and others (1981) reported that Grass Carp larvae consumed benthic invertebrates (primarily chironomid larvae) and zooplankton until they reach about 55 mm TL. Edwards (1973) reported age-0 Grass Carp consumed oligochaetes, mayflies, caddisflies, amphipods, and chironomids. Fry of Rainbow Trout (Oncorhynchus mykiss) and Common Carp were eaten by young Grass Carp (even in the presence of preferred plants), but Grass Carp would not eat the eggs of either species (Edwards, 1973; Singh and others, 1976). Grass Carp larger than 25 cm did not feed on fry in the laboratory (Singh and others, 1976). The size at which Grass Carp begins to feed on plants depends on temperature, with smaller fish switching to plants in warmer waters (Stanley and others, 1978). Adults feed on a variety of aquatic macrophytes, such as water hyacinth (Eichhornia crassipes), eelgrass (Vallisneria americana), cattails (Typha spp.), and Hydrilla spp. (Collee and others, 1978; reviewed in Opuszynski and Shireman, 1995; Cassani, 1996). In some cases, Grass Carp will consume animals when plant material is lacking (Nikol'skiy and Aliyev, 1974; Forester and Avault,1978). Alternatively, Grass Carp may consume terrestrial macrophytes in the absence of aquatic vegetation (Kilgen and Smitherman, 1971; Terrell and Fox, 1974). Kilgen and Smitherman (1971) reported that individuals raised their heads clear of the water to consume terrestrial macrophytes. The species is a voracious herbivore that can quickly eliminate large volumes of vegetation (Mitzner, 1978). Although some reports indicated that removal of aquatic vegetation by Grass Carp was advantageous for some game fishes (for example, Maceina and others, 1991), such habitat modification could result in habitat loss for native fishes, birds, and invertebrates (Gasaway and Drda, 1977; Forester and Avault, 1978; Ware and Gasaway, 1978; Laird and Page, 1996; Ross, 2001).
The Grass Carp is native to rivers of eastern Asia, from the Amur River of far eastern Russia and China, south to the West River of southern China (Shireman and Smith, 1983; Li and Fang, 1990).
The Grass Carp was first brought into the U.S. in 1963, when it was imported by aquaculture facilities in Alabama and Arkansas. Subsequently, it was widely stocked for vegetation control (Courtenay and others, 1984; Fuller and others, 1999). Escapes from aquaculture facilities, intentional stocking (both legal and illegal), and movement of introduced populations have expanded its range. The species is now known from almost every state, and is established in the Mississippi, Missouri, and Ohio rivers, as well as the smaller Trinity River (Texas).
Plate 4. Distribution of Grass Carp in the United States. See Methods for details regarding data
Commercial fisherman with Grass Carp netted from
Grass Carp, Caloosahatchee River,
Grass Carp, Caloosahatchee River,
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