Genus Ctenopharyngodon
Steindachner, 1866

The grass carp genus contains only a single species found in East Asia but widely introduced for food and its ability to digest macrophytes.

This genus is characterised by a rounded body and broad head, the eyes are large and positioned at or above the body axis and often visible from the underside of the head, mouth wide and terminal, no barbels, moderate-sized scales, a complete lateral line, dorsal and anal fins short and lacking spines, branchial membranes attached to the isthmus, short unfused gill rakers, brown to black peritoneum, and pharyngeal teeth in 2 rows with the crowns strongly compressed and serrate and with a longitudinal groove on the grinding surface.

Ctenopharyngodon idella
(Valenciennes in Cuvier and Valenciennes, 1844)

Common names

كپور علفخوار (= kapour-e alaf khaar or alaf khoar or kopur 'laf khoar, carp grass-eater or grass-eater), آمور (= amur), سفيد پرورشي (safid parvareshi or mahid safid parvareshi meaning cultured white fish, from a resemblance to mahi safid, i.e. Rutilus frisii kutum).

[grass carp, white amur].

Systematics

Leuciscus idella was originally described from China. A hybrid of this carp and Rutilus frisii has been bred at the Astaneh Ashrafie Fisheries Research Station and named "Samur" (Iranian Fisheries Research and Training Organization Newsletter, 11:6, 1996). See under Rutilus frisii for more information.

Key characters

This species is identified by the eyes being low on the side of the head, the anal fin is far back on the body close to the caudal fin, and pharyngeal teeth have large, parallel grooves on the grinding surface.

Morphology

Lateral line scales 34-47. Scales have a wavy anterior edge, central focus and moderate numbers of anterior and posterior radii. Dorsal fin branched rays 6-8, usually 7, after 3 unbranched rays, anal fin branched rays 7-9, usually 8, after 3 unbranched rays, pectoral fin branched rays 13-20 and pelvic fin branched rays 7-8. Gill rakers number 15-18 and touch the adjacent raker when appressed. Vertebrae 40-47. Pharyngeal teeth are 2,5-5,2, 2,4-5,2, 2,4-4,2, or 1,4-5,2 and are obviously serrated with a longitudinal grooves. The gut is long and complexly coiled. The diploid chromosome number is 48, the triploid 72 (Klinkhardt et al., 1995; Nowruzfashkhami et al., no date). Serum immunoglobulins have been characterised by Soltani et al. (2003).

Sexual dimorphism

Nuptial tubercles are evident on the male head, upper caudal peduncle, dorsal and caudal fins and in particular on the pectoral fins, the first ray of which is thickened, while the female has a distended belly and a swollen and pinkish vent.

Colour

The back is dark, olive to greenish-brown, the flanks are silvery but scales are marked with darker pigment on their posterior margin giving the appearance of a row of spots, and the belly is white to cream-yellow. Scale centres may reflect golden or yellowish tints. Upper scales are outlined with dark pigment to give a cross-hatching effect. The fins are grey-green, or grey to black, except the pelvics which resemble the belly colour. Peritoneum brownish black.

Size

Reputed to attain 1.6 m and about 50 kg in its native range; reports of weights up to 180 kg probably being exaggerations. Reaches 80 cm in the Tadjan River near Sari (A. Abdoli, pers. comm., 1995).

Distribution

The native distribution is in East Asia but it has been introduced to Iranian waters. Also introduced to Afghanistan, Pakistan, and Iraq (Shireman and Smith, 1983).

This species was first introduced in the 1950s according to Armantrout (1980) in the Anzali Mordab for vegetation control, adults surviving to the 1960s but no breeding population was established. Also introduced in 1966 from a hatchery in the Krasnodar region of the former U.S.S.R. and stocked in the Anzali Mordab (Anonymous, 1970b) and in October 1970 50,000 fingerlings from the U.S.S.R. were introduced to the Caspian Sea and Anzali Mordab (Griffiths et al., 1972). Three large fish (80 cm) were caught in January 1971 and believed to be from the October introduction and evidence of good growth although they may have been from an earlier stocking. It is reported from the Siah-Keshim Protected Region of the Anzali Mordab (Riazi, 1996), presumably recently stocked, and is stocked in a variety of reservoirs in the provinces of Gilan and Mazandaran but not as widely as silver carp (Hypophthalmichthys molitrix). It is pen cultured in Gomishan Reservoir, Mazandaran (Madbaygi, 1993b). Grass carp were introduced to Khuzestan in the 1970s to control vegetation in irrigation ditches. In April 1974, 1150 fish were released in the Dez Irrigation Project (Saadati, 1974). It is reported from Mahabad Dam (Abdi, 1999; www.mondialvet99.com, downloaded 31 May 2000), from the Safid River and Anzali Talab (Abbasi et al., 1999), from Lake Zaribar, Kordestan (Abzeeyan, 5(5):III, 1994), the Kor River in Fars (A. Alamdari, in litt., 1997), from the Sistan basin in Hamun Sabari, Hamun Kushk and the canal flowing into Chahnimeh (Ahmadi and Wossughi, 1988; Mansoori, 1994; J. Holčík, in litt., 1996), from the Haft Barm lakes near Shiraz in 1984 although these later disappeared, possibly eaten by introduced Sander lucioperca (Petr, 1987). As escapees from a fish farm, they have been found in Lake Famur. Also recorded from the Gorgan, Tajan and Safid rivers, and the Anzali Mordab (Kiabi et al., 1999), and it is mapped from the Kor, Yazd, Hormuz, Lut and Sistan basins without exact localities; the Kashaf River in the Tedzhen River basin; middle reaches of the Atrak River, lower reaches of the Gorgan, Neka, Babol, Heraz and Safid rivers and in the Anzali Mordab, all in the Caspian Sea basin, the middle to lower Talkheh and lower Zarrineh rivers in the Lake Orumiyeh basin, the middle to lower Abhar-Shur and Qom River in the Namak Lake basin, the middle to lower Zayandeh River in the Esfahan basin; the lower Karun and Jarrahi rivers in the Tigris River basin, and the lower Jovein and middle Kal Shur rivers in the Kavir basin (Abdoli, 2000).

It was introduced to the Soviet Caspian Sea in 1970-1974 where small populations became established in the Terek River and the Volga delta and to the Karakum Canal and Kopetdag Reservoir of Turkmenistan near the Iranian border (Baltz, 1991; Shakirova and Sukhanova, 1994; Sal'nikov, 1995; Opuszynski and Shireman, 1995).

Grass carp could establish breeding populations in the large rivers of southern Iran and Iraq if the environment proves favourable and there is enough uninterrupted river flow for eggs to hatch.

Zoogeography

This species is an exotic in Iran and has a native range from the Amur River basin of Siberia south to southern China. It has been widely introduced around the world for vegetation control.

Habitat

The natural habitat is large rivers but this species adapts easily to pond culture. Grass carp can live in the Caspian Sea at salinities of 5-8‰ although a few are found at 10-12‰. They enter rivers to spawn (Abdusamodov, 1986). Temperatures in the range 0-41°C and low oxygen concentrations (0.2 mg/l) are tolerated by this species as is high turbidity. Fry have an upper lethal temperature range of 33-41°C and temperatures greater than 38°C are lethal for adults. pH range is 5.0-9.0. Adults prefer densely vegetated inshore areas with depths of 1-3 m. Adults leave the river after spawning and feed in lakes, reservoirs and on floodplains, returning to the river in autumn to overwinter in deep holes separate from the juveniles. Young hide in vegetation of lakes, reservoirs and floodplains. Juveniles may migrate as much as 1000 km up- or downstream from the original spawning site in their native habitat. Young fish overwinter in deep holes in river beds.

Age and growth

Growth rate in Khuzestan canals was 1.8 g per day while in ponds growth was 6.6 g per day when fed alfalfa during a 5-month growing season from April to September (Saadati, 1974; Behnke, 1975a). Males begin to mature at 4 years and females at 5 years in the Terek River of Dagestan (Abdusamadov, 1986). Maturity is attained at 6-10 years in the Amur River, the native habitat, and as early as 10 months in Malaysia. Life span is over 33 years. Growth rate in this species is perhaps greater than in any other fish. Growth to 1 kg in the first year of life and 2-3 kg per year thereafter in temperate areas is very high; in tropical areas a 20 g fingerling can reach 8.5 kg in 1 year. Rates of 10-22 g per day have been reported in various areas of the world depending on local conditions.

Food

Grass carp are herbivores, except for quite small fish (20 mm total length or less) which consume zooplankton. In Khuzestan, the grass carp prefers to eat Potamogeton spp. and Alisma gramineum to Chara and Cladophora (Saadati, 1974). The grass carp can consume 100-150% of its body weight per day of aquatic vegetation. Peak feeding occurs at 25-30°C but food is taken in the range 15-35°C. Grass carp stocked in the Anzali Mordab and fish farms of the Caspian Sea basin consume fresh Azolla, an introduced fern. Grass carp stocked at 800/ha consume 400-500 kg of Azolla daily gaining 800-1200 g in 5 months. In China this species is known to eat grass, leaves, small fishes, insects and other items in addition to aquatic vegetation or when such vegetation is in low supply. About half the plant food passing through the digestive system is undigested and large quantities of plant material must be eaten to sustain life. This consumption rate is the reason for its success at aquatic vegetation control (Greenfield, 1973). Grass carp overwinter without feeding.

Reproduction

A spawning migration to a large river takes place at about 15-17°C water temperature. The female swims in the centre of the river at the surface accompanied by 2-3 males, they roll and rub their bodies together and often jump out of the water. A male prods the female's body to stimulate egg release and leans closely to one side. Eggs are semi-buoyant and require a slow and steady current to keep them off the bottom (minimum water velocity of 0.23 m/second or more to support them and allow hatching; this is found in large rivers where the eggs hatch as they drift downstream; at 20°C and a not unusual velocity of 1.2 m/second, hatching requires 180 km of river). Temperatures should be above 20°C and preferably 21-25°C, or 26-30°C in another source. At these temperatures hatching takes about 40 hours. Flow rates should be 0.7-1.8 m/sec. Spawning occurs after heavy rain in rising rivers, when turbidity may reduce predatory attacks on the semi-pelagic eggs (Greenfield, 1973). This regime is also required for newly hatched fry and such conditions are rare outside their native habitat. In the Terek River of the Caspian Sea basin, the spawning migration begins in mid-April at water temperatures of 15-17°C and continues until August although numbers begin to decrease from the end of May. Spawning takes place after a sharp rise in water level and current speed. Eggs are first found in the drift in the second week of June and hatch 34-70 hours later depending on temperature. Some larvae reach rice fields and live there until autumn when the fields dry up, some being lost, others migrating. Other larvae are carried into the Caspian Sea where they are sensitive to the prevailing salinity at 1-1.5 days old (Abdusamadov, 1986). Up to 100,000 eggs are laid at one time (Greenfield, 1973) and in the Terek River fecundity reaches 1,230,700 eggs (Abdusamadov, 1986). Absolute fecundity may reach 2 million eggs. Eggs are up to 2.5 mm in diameter before fertilisation and are greyish-blue to bright orange. In water they swell to over 5.3 mm in 2 hours, becoming buoyant in flowing water.

Parasites and predators

Mokhayer (1976b) reports the cestode Bothriocephalus gowkongensis and the acanthocephalan Pomphorhynchus perforator. Red-sore disease is reported from fish pond grass carp in Iran by Razavilar et al. (1981). It is caused by a bacterium Aeromonas hydrophila and treatment was unsuccessful. Mokhayer (1989) records metacercariae of the eye fluke, Diplostomum spathaceum from this species in Iran, which can cause complete blindness and death in commercially important species, as well as shedder scales (sic), Echinochasmus perfoliatus. Jalali and Molnár (1990b) record the monogenean Dactylogyrus lamellatus from this species at fish farms in Iran. Viral haemorrhagic disease has been reported from grass carp in Iran (Iranian Fisheries Research and Training Organization Newsletter, 6:6, 1994; 9:6, 1995). Pond-cultured grass carp were found to be infected by the tapeworm Bothriocephalus, with 70-80 parasites causing intestinal obstruction and lowered haemoglobin, haematocrit and erythrocyte values (Esmaeli and Abbasi, 1996). Esmaeli and Peighan (1997) record an Aeromonas-like bacteria from grass carp in Khuzestan Province. Ebrahimzadeh Mousavi and Khosravi (1999; www.mondialvet99.com, downloaded 31 May 2000) record the toxigenic fungi Aspergillus flavus, Alternaria, Penicillium and Fusarium from this species and the pond water at a fish farm in northern Iran. The crustacean parasite Lernaea elegans is reported from this species in the Mahabad Dam reservoir (Abdi, 1999; www.mondialvet99.com, downloaded 31 May 2000). The intestinal helminth Bothriocephalus gowkongensis was recorded from this species on fish farms in West Azarbayjan Province (Azarvandi et al., 1999). Naem et al. (2002) found the following parasites on the gills of this species from the western branch of the Safid River, namely the protozoan Ichthyophthirius multifilis, a copepod crustacean Lernaea sp., monogenean trematodes Dactylogyrus lamellatus, D. ctenopharyngodonis, and Gyrodactylus sp.. Jalali et al. (2002) and Jalali and Barzegar (2006) record Diplostomum spathaceum and Dactylogyrus lamellatus from this species in Lake Zarivar. Esmaeili et al. (2005) found a Flavobacterium columnaris-like bacterium on grass carp form Khuzestan fish ponds, suspected of either causing a 40% mortality or being a secondary factor in the fish kill. Pazooki et al. (2005) record Ergasilus peregrinus from this species in waterbodies of Zanjan Province. Araghi Soureh and Jalali Jafari (2006) recorded Dactylogyrus lamellatus from this species in the Mahabad River of the Lake Orumiyeh basin. Barzegar and Jalali (2006) report parasites in this species from Kaftar Lake as Trichodina sp., Dactylogyrus lamellatus, Lernaea cyprinacea and Diplostomum spathaceum.

Any piscivore will take this species.

Economic importance

This species has been introduced to Iran to control aquatic weeds in drainage and irrigation canals as an alternative to using polluting chemicals or mechanical removal. In some countries at is sought after by anglers. Grass carp may also help to control the snail-carried, human disease schistosomiasis, since the vegetation on which the snails live is severely reduced. They are also a food fish which relies on food sources not available to native fish (few fish consume whole plants). Grass carp consume vegetation at a rate of 100:1, i.e. for every 1 kg increase in grass carp biomass 100 kg of vegetation is consumed. Removal rates may exceed this figure since leaves are bitten off and branches clipped with not all of it being consumed. In the Dez Irrigation Project large amounts of this vegetation were removed daily from screens in test sections. Stocking in the Dez Irrigation Project in Khuzestan showed a removal rate approximately the same as mechanical control (Saadati, 1974; Behnke, 1975a). During a 5 month period the grass carp controlled 250 tons of aquatic vegetation per hectare. The fish preferred plant species which blocked the canals (Potamogeton spp. and Alisma gramineum) rather than those which grew close to the substrate (Chara and Cladophora) and did not interfere with water flow. Shireman and Smith (1983) give details on artificial propagation of this species.

Esmaeilzadeh et al. (2004) studied the nutrient composition and marinade qualities of this fish in Iran and compared them to those for safid mahi (Rutilus frisii) and found them to be preferable according to the organoleptic properties. The marinades could be stored for 6 months at 10ºC.

Fish farming of this species in Sistan was discontinued as its consumption of vegetation was reducing food for other species (www.netiran.com, downloaded 28 February 2005).

Holčík and Oláh (1992) report a catch of 315 kg in the Anzali Mordab in 1990. However Iran acounts for almost all the production of grass carp in the Near East and North Africa (4378 tonnes in 1994) (Food and Agriculture Organization, Fisheries Department, 1996). The aquaculture production in 1995 was 3942 tonnes (Bartley and Rana, 1998b). Grass carp sold for about U.S.$2.00/kg in 1995 (Rana and Bartley, 1998a). Marjan Iran Company was selling 1500-2000 g fish for U.S.$2.10/kg in August 2003 (http://groups.yahoo.com/groups/hilsa/message/25).

The inland waters of Turkmenistan had catches of 23 to 29.7 tonnes for the years 1971-1974 and a catch of 76 tonnes in 1970 when a ban on taking phytophagous fish was lifted.

Greenfield (1973) reviews the advantages and disadvantages of using this species as a weed control agent in the U.S.A. and Charyev (1984) in the Kara-kum Canal in Turkmenistan. Destruction of habitat for fishes and waterfowl, competition with native species and introduction of exotic diseases and parasites are all problems once this fish escapes into a main river suitable for reproduction. Their destruction of plants may interfere with waterfowl management, destroy breeding grounds for other species and facilitate the attacks of predators. Ideally triploids, produced by cold or warm shocks or by hydrostatic pressure on fertilised eggs, should be used initially as they cannot reproduce (Clugston and Shireman, 1987). However the chromosome number of each fish must be checked (by electronically measuring the volume of a red blood cell nucleus) as the process is not 100% effective. Grass carp are reproducing naturally in the Kara-kum Canal, vegetation is controlled, fish stocks have increased and some reduction of mosquitos has been obtained. However the ecosystem has been changed, spawning grounds of commercial species threatened, undesirable species have been introduced accidentally, and reduction in vegetation affects water quality. Grass carp are best used in restricted areas where improved flow and reduced mosquito populations are required but where there is no commercial fishery (Charyev, 1984).

The grass carp has a short gut and about half the plant material eaten is released to enrich the water and promote algal blooms. Oxygen levels and water clarity are reduced. The removal of plants can remove food sources for other fishes, shelter and spawning substrate. Additionally, as noted, the triploid treatment is not always effective and the species can become established.

Iran has had problems with disease outbreaks and poor survival of fingerlings which has led to production problems (Shehadeh, 1997).

Robins et al. (1991) list this species as important to North Americans. Importance is based on its use in aquaculture, as food and in textbooks. There are numerous studies on this species as an experimental fish and in relation to aquaculture. Some Iranian studies include Morovvati et al. (2006) on seasonal changes of pronephros lymphoid tissue; Nahavandi et al. (2006) on the chemiluminescent response to determine the effect of various concentrations of diazinon, an organophosphate, on phagocytosis in order to measure immunity after exposure to this toxin; Pourgholam et al. (2006) and Sharifpour et al. (2006) on the toxicity and histopathological effects of diazinon; Sharifpour et al. (2006) on the sub-lethal effects  of diazinon on various organs; Pourgholam et al. (2006) and Soltani and Pourgholam (2007) on the toxicity of diazinon and the effects of sub-lethal concentrations on haematological, biochemical indices and lysozyme activity; Safari (2008) on dietary lipid level on growth, feed utilisation and body composition of juveniles; etc.

Conservation

No conservation is required for this exotic species. Krasznai (1987) and Petr (1987) give details of fish farms propagating this species in Iran. For example, 10 million were produced in the Safid Rud Fish Farm in 1986. 20 million carp, silver carp and grass carp fingerlings were produced in the Shahid Rajaae Hatchery in Sari for release across Iran in reservoirs and dams (Abzeeyan, Tehran, 4(7):VII, 1993). Feeding and growth studies on this species have also been carried out on this species in the Shaid Rajaee Hatchery (Ahmadi and Rezai, 1998). Experiments on induction of triploidy have been carried out in Iran using cold and heat shocks (M. Hassanzadehsaber, M. Pourkazemi, M. R. Nowruzfashkhami and A. Ghanaatparast (www.meeresschule.com/cgi-bin/abstracts/gastbuch.asp, downloaded 17 January2005).

Further work

Studies on the interactions of this species and native Iranian taxa should be carried out and introductions carefully controlled and monitored.

Sources

Shireman and Smith (1983) give a summary of the biology of this species. There is an extensive literature on herbivorous fishes, a recent book being Opuszynski and Shireman (1995), which has sections on grass carp. Gholipour (1996) has an account in Farsi.

Comparative material: BC65-381, 2, 95.4-98.8 mm standard length, Singapore, fish ponds (no other locality data).

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