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<br />36 Foreign Nonindigenous Carps and Minnows (Cyprinidae) in the U.S.-A Guide to their Identification <br /> <br />Ecology <br /> <br />The Grass Carp is a large species that can attain a <br />weight of 45 kg (Robison and Buchanan, 1988; Etnier <br />and Starnes, 1993) and a length of 1.5 m TL (Laird <br />and Page, 1996). Typical longevity is about 5-11 years <br />(Berg, 1964), but an individual in the Amur River was <br />estimated to be 21 years, based on scale growth rings <br />(Gorbach, 1961). Growth is relatively rapid, especially in <br />the tropics where it can average 109 per day (Hickling, <br />1967). <br />Typical habitat includes quiet waters, such as lakes, <br />ponds, pools, and backwaters of large rivers, and indi- <br />viduals generally do not travel long distances except for <br />the annual spawning migration (Mitzner, 1978; Nixon <br />and Miller, 1978; Bain and others, 1990). Nevertheless, <br />there are reports of juvenile Grass Carp traveling as <br />far as 1,000 km from their original spawning grounds <br />(Stanley and others, 1978). Shallow water is the gener- <br />ally preferred habitat, although deeper waters are used <br />when temperatures decrease (Nixon and Miller, 1978). <br />A number of experimental studies have reported envi- <br />ronmental tolerances for Grass Carp. Fry and fingerlings <br />have been reported to tolerate water temperatures from <br />0-40 oC (Stevenson, 1965; Vovk, 1979), and Stevenson <br />(1965) reported that fingerlings in small ponds in <br />Arkansas survived 5 months under heavy ice cover. <br />Chilton and Muoneke (1992) reported an upper lethal <br />temperature range for fry as 33-41 oC, and for yearlings <br />as 35-36 oc. Bettoli and others (1985) documented a <br />thermal maximum of 39.3 OC and a preferred tempera- <br />ture of 25.3 oc. Collee and others (1978) reported that <br />feeding declined sharply below 14 oc. Nico and others <br />(2005) reviewed temperature tolerance of Grass Carp <br />and the other Chinese carps. <br />Oxygen consumption (per gram of body <br />mass) increases with higher water temperature and <br />decreases with fish age and mass (Chen and Shih, <br />1955; Wozniewski and Opuszynski, 1988). The <br />lethal low oxygen level for juveniles was <0.5 mg/L <br />(Negonovskaya and Rudenko, 1974). The maximum <br />pH for culture of Grass Carp was reported as 9.24 <br />(Liang and Wang, 1993). Egg hatching was delayed <br />below pH 6.5 and increased mortality and deformation <br />of larvae occurred below pH 6.0 (Li and Zhang, 1992). <br />Sensitivity to low pH decreased with age (Li and Zhang, <br />1992). Median lethal concentration of ammonia was <br />determined to be 1.05 mg/L (Gulyas and Fleit, 1990). <br />The Grass Carp appears to be tolerant of low levels <br />of salinity, and may occasionally enter brackish-water <br />areas. Fry (32-50 mm TL) survived transfer from fresh- <br /> <br />water to a salinity of 12 ppt (Chervinski, 1977). Adults <br />(2+ years) survived 10.5 ppt salinity for about 24 days <br />and 17.5 ppt for 5 hours (Cross, 1970). However, Grass <br />Carp acclimated to 3, 5, and 7 ppt had an upper tolerance <br />of about 14 ppt (Kilambi and Zdinak, 1980). Maceina <br />and Shireman (1980) showed that fingerlings reduce <br />feeding at 9 ppt and stop feeding altogether at 12 ppt; <br />thus, they predicted Grass Carp could inhabit brackish- <br />water bodies up to 9 ppt. Maceina and Shireman (1979) <br />reported that the species can tolerate 14 ppt for as long <br />as 4 days, but that the upper long-term tolerance of <br />fingerlings to saline waters was lower, about 10-14 ppt. <br />Maceina and others (1980) noted that oxygen consump- <br />tion decreased along a salinity gradient of 0-9 ppt. <br />Movement of Grass Carp from one river to another <br />through a brackish-water estuary (Pavlov and Nelovkin, <br />1963, in Cross, 1970) is not surprising given the species' <br />tolerance to low levels of salinity. Avault and Merowsky <br />(1978) reported food preference and salinity tolerance of <br />hybrid Common Carp X Grass Carp. <br />The species is probably best known for its raven- <br />ous appetite for plant matter (especially macrophytes); <br />however, small Grass Carp feed on invertebrates before <br />switching to plants. Watkins and others (1981) reported <br />that Grass Carp larvae consumed benthic invertebrates <br />(primarily chironomid larvae) and zooplankton until they <br />reach about 55 mm TL. Edwards (1973) reported age-O <br />Grass Carp consumed oligochaetes, mayflies, cadd- <br />isflies, amphipods, and chironomids. Fry of Rainbow <br />Trout (Oncorhynchus mykiss) and Common Carp were <br />eaten by young Grass Carp (even in the presence of <br />preferred plants), but Grass Carp would not eat the eggs <br />of either species (Edwards, 1973; Singh and others, <br />1976). Grass Carp larger than 25 em did not feed on <br />fry in the laboratory (Singh and others, 1976). The size <br />at which Grass Carp begins to feed on plants depends <br />on temperature, with smaller fish switching to plants <br />in warmer waters (Stanley and others, 1978). Adults <br />feed on a variety of aquatic macrophytes, such as water <br />hyacinth (Eichhornia crassipes), eelgrass (Vallisneria <br />americana), cattails (Typha spp.), and Hydrilla spp. <br />(Collee and others, 1978; reviewed in Opuszynski and <br />Shireman, 1995; Cassani, 1996). In some cases, Grass <br />Carp will consume animals when plant material is lack- <br />ing (Nikol'skiy and Aliyev, 1974; Forester and Avault, <br />1978). Alternatively, Grass Carp may consume terres- <br />trial macrophytes in the absence of aquatic vegetation <br />(Kilgen and Smitherman, 1971; Terrell and Fox, 1974). <br />Kilgen and Smitherman (1971) reported that individuals <br />raised their heads clear of the water to consume terres- <br />trial macrophytes. The species is a voracious herbivore <br />