Silver Carp, Hypophthalmichthys molitrix
The Silver Carp, Hypophthalmichthys molitrix, whose common Spanish name is carpa plateada, is a species in the Carp and Minnow or Cyprinidae Family, known collectively as carpas and carpitas in Mexico. This fish is also known by the common name Flying Carp (with good reason!). Globally, there are only three species in the genus Hypophthalmichthys, two of which are farmed in Mexico and also found in most freshwater systems in Mexico. The Silver Carp dates to the Chinese Tang Dynasty, 7th to 10th century, and was imported to North America in the 1970s to control algae growth in reservoirs and municipal waste water treatment facilities and for aquaculture. They quickly escaped captivity and today are considered a highly invasive species that is causing major destruction of habitat. Pound for pound they are the number one species produced globally via aquaculture. They are currently present in eighty-eight countries.
The Silver Carps have elongated and laterally compressed bodies that are widest near the dorsal fin origin. Younger fish are silvery in color; as they age, they fade to olive-green dorsally and silvery ventrally. Their fins are dusky with the caudal fin being darker than the others. Their large head has a large terminal mouth, small eyes found far forward on the midline of the body, and an overhanging front jaw. Their mouth extends to the margin of the eyes. Their anal fin has 13 to 15 rays; their caudal fin is forked; and their dorsal fin has 8 rays and originates posteriorly of the pelvic fin base. They have a ventral keel that extends from the isthmus to the anus. Their body is covered with small scales.
The Silver Carps are deep-bodied freshwater fish found in backwater areas of large streams, rivers, and water reservoirs with dense aquatic vegetation. The current world record was caught in Germany in 2003, that was 1.3 meters (4 feet 3 inches) in length and 48.5 kg (106 pounds 10 ounces) in weight. They are filter feeders consuming phytoplankton, zooplankton, and detritus. They significantly increase the turbidity of the water body in which they reside by their bottom feeding. They are found in temperate waters with temperatures between 6oC (43oF) and 28oC (82oF) and can tolerate salinities up to 12 ppt and low dissolved oxygen. Reproduction involves external fertilization with released eggs being quickly fertilized by males. Each female can release up to five million eggs per year. After hatching, the eggs either reside on the bottom or float midwater, thus requiring a water flow to remain suspended. They are non-migratory and have a lifespan of up to 20 years. They are highly invasive and currently present in twelve states of the mid-western United States. Millions of dollars are currently being spent to try to keep them from entering the Great Lakes systems via the Chicago Sanitary and Ship Canal. One concern is that they are transported and introduced to new water systems by fishermen who use them as live bait. The importation of live fish and/or their use as live bait is currently banned in several states in the United States. There is a major ongoing effort to remove all wild Silver Carp from the United States.
In Mexico, they are second to the Common Carp as a farmed carp with explosive growths in production occurring over the last 10 years. They currently have a wide distribution being farmed in the states of Aguascalientes, Chiapas, Chihuahua, Coahuila, Durango, Guanajuato, Hidalgo, Jalisco, Mexico, Michoacán, Oaxaca, Puebla, Querétaro, San Luis Potosí, Sonora, Tlaxcala, and Zacatecas. The farming of Silver Carps is more economical than with other carps as they do not require expensive formulated feed, are environmentally friendly, and provide a low-priced source of animal protein. Global production levels are currently at ten million tons per annum and doubling every ten years. Also seeds are readily available from artifical breeding, without reliance on natural resources. They grow and mature faster than other carps but require a great deal of space and plentiful food sources to survive. The majority of current research on this species focuses on integrated farming in small-scale aquaculture in developing countries.
The Silver Carp is also called the Flying Carp due to its tendency to go airborne when startled. It is capable of leaping 10 feet into the air – see for example – https://www.youtube.com/watch?v=YtFJ7IvQ-dE!). They have also been featured in an episode of River Monsters.
The Silver Carp is similar to and can be confused with the Bighead Carp, Hypophthalmichthys nobilis, but has smaller eyes set low on the body and a keel that extends forward past the pelvic base. It also lacks the dark blotches and large non-pointed head characteristic of the Bighead Carp.
The Silver Carps are used on a limited basis with marginal results for controlling noxious blue-green algae (cyanobacteria) in numerous water bodies. As a result, they are in direct competition with all native species that depend on zooplankton for survival including the Bigmouth Buffalo, the Gizzard Shad, and the Paddlefish. They are very difficult to catch via hook and line because of their dietary habits. The most effective way to catch them is via a “suspension method”, consisting of a large dough ball that disintegrates slowly, surrounded by a nest of tiny hooks that are embedded in the bait. The entire apparatus is suspended below a large bobber. The fish feed on the small particles released from the dough ball and will bump against it with the intention of breaking off more small particles that can be filtered from the water, eventually becoming hooked on the tiny hooks. They are also caught by bowfishermen via “snagging” with large weighted treble hooks, either while in the water or when airborne, or simply by catching flying fish from boats with nets. They are marketed alive and fresh close to where they are raised and are generally the lowest priced fish in the market. There is virtually no export market established for this species. Some of the larger Silver Carps contain algal toxins built up in their systems and are hazardous to eat.