Grass Carp

Grass Carp, Ctenopharyngodon idella

The Grass Carp, Ctenopharyngodon idella, whose common Spanish name is carpa hervibora, is a species in the Carp and Minnow or Cyprinidae Family, known collectively as carpas and carpitas in Mexico. This is the only species in the genus Ctenopharyngodon and it is found in the majority of Mexico’s freshwater systems.

The Grass Carps have elongated torpedo-shaped cylindrical bodies. They are silvery dark olive dorsally and transition to brownish-yellow on their sides and to white ventrally. Their head has a very short snout. Their slightly oblique mouth opens at the front and is equipped with broad ridged pharyngeal teeth in two rows. They have no barbels. Their anal fin is found closer to the caudal fin than in most other cyprinids and has three spines and 7 to 11 rays. Their dorsal fin has 3 spines and 7 or 8 rays. They have a complete lateral line and large well-defined scales.

The Grass Carps are freshwater fish that thrive in small lakes that are full of aquatic vegetation. They reach a maximum length of 1.4 meters (4 feet 6 inches) and weight of 45 kg (99 pounds). They have voracious appetites being capable of consuming three times their body weight per day. They have exceedingly rapid growth rates and can double their length in six months.

The Grass Carps are native to eastern Asia and were introduced to Mexico in 1960 and to the United States in 1963 for aquatic weed control. They quickly escaped via widespread authorized, illegal, or accidental introductions and are now found in 45 states within the United States. They feed primarily on aquatic plants but also consume detritus, insects, and invertebrates. They have great tolerance for temperature changes and can survive in water temperatures from 0oC (0oF) to 38oC (104oF) but require water temperatures between 20oC (68oF) and 30oC (86oF) and access to fast moving rivers for spawning. They can also tolerate relatively high saline and low oxygen levels. Although present in many North American freshwater systems, they fail to breed and establish populations on their own indicative that they have quite specific reproductive requirements. These include long rivers with gravel bottoms for the survival of pelagic eggs (which hatch in 2 to 3 days) and very young fish. They have a lifespan of up to fifteen years in the wild.

The Grass Carps constitute the top aquaculture species globally with over five million tons produced per year, which is growing exponentially. Mexico is produces approximately 30,000 tons of fish annually. They are raised in ponds, cages, and pens with the principal farms located in the states of Mexico, Hidalgo, Tamaulipas, and Jalisco. Their introduction in many countries unfortunately also brought with it the parasitic tapeworm Bothriocephalus opsarichthydis. Due to their highly invasive nature they have had significant adverse ecological impacts post-introduction. These include alteration of the food web by changing plant, invertebrate, and fish communities via the removal of food, shelter, and spawning substrate. For example one Grass Carp will consume 45 kg of plant material per day expelling about half into the water thus enriching it and promoting algal blooms, which in turn reduces water clarity and decreases oxygen content. They are mostly sold domestically at an average of 50 cents per pound with very few exports due to their low prices. Major improvements in the farming of the Grass Carp have recently been made including enhanced breeding technologies, the development of low cost feeds, and the development of disease control.

For recreational anglers the Grass Carps are considered a strong foe by rod and reel, however, they are difficult to catch due to their vegetarian diets. They are also popular among bowfishermen. They are normally sold either live or freshly dressed with as many as 15 value-added commercial products offered from a single fish. They are considered an invasive species that is hard to eradicate (a process that started shortly after their introduction) and can quickly become a pest that threatens local biodiversity. For anglers this species runs the gambit from “hated trash fish” (North America) to “fabulous new sportsfish and table fare” (Europe). If you catch one, take it home, and prepare it for a feast, but keep in mind that the flavor of the meat is directly related to the quality of the water it is taken from. If you don’t like its taste, simply use as garden fertilizer or cat food. There will be plenty more where that one came from!

Grass Carp (1)Grass Carp, Ctenopharyngodon idella. Fish caught from the Big Muddy River, Fenton, Illinois, April 2016. Length: 19.0 cm (7.5 inches). Catch, photo, and identification courtesy of Ben Cantrell, Peoria, IL.

Grass Carp (2)Grass Carp, Ctenopharyngodon idella. Fish caught from the Illinois River, Peoria, Illinois, April 2016. Length: 84 cm (33 inches). Catch, photo, and identification courtesy of Ben Cantrell, Peoria, IL.