Montana Field Guide

The silver carp (SICA) is a deep-bodied fish that is laterally compressed (Berg 1949; Nico et al. 2018). They are a very silvery color when young and when they get older they grade from a greenish color on back to silver on the belly (Berg 1949; Nico et al. 2018). They have very tiny scales on their body, but the head and opercules are scaleless (Berg 1949; Nico et al. 2018). They have a large mouth without any teeth in the jaw, but they have pharyngeal teeth (Berg 1949; Nico et al. 2018). The eyes of SICA are situated far forward on the midline of the body and are slightly turned down (Berg 1949; Nico et al. 2018).

Juvenile fish lack spines in their fins (Berg 1949; Nico et al. 2018). Metalarvae and early juvenile are similar to bighead carp (Hypophthalmichthys nobilis) but the pectoral fin extends only to the base of pelvic fin (as opposed to beyond the pelvic fin in bighead) (Berg 1949; Nico et al. 2018). The species is known for leaping out of the water when startled by noise such as from boats (Berg 1949; Nico et al. 2018).

SICA are unlikely to be confused with our native cyprinids due to their size (up to 1 m in length and 27 kg) and the unusual position of the eye (Berg 1949; Nico et al. 2018). They most closely resemble bighead carp (Hypophthalmichthys. nobilis) but have a smaller head, an upturned mouth without teeth, a keel that extends forward past pelvic fin base, lack the dark blotches characteristic of bighead carp and have highly branched gill rakers (Berg 1949; Nico et al. 2018).

In its natural range, Silver Carp migrate upstream to breed in communal spawning grounds during spring flooding; egg and larva float downstream to floodplain zones (Higbee et al. 2004).

Silver Carp are primarily a species of large rivers, they can tolerate salinities up to 12 ppt and low dissolved oxygen (3mg/L) (Nico et al. 2018). Silver Carp feed on both phytoplankton and zooplankton (Radke and Kahl 2002). Pflieger (1997) considered the impact of this species difficult to predict because of its place in the food web. In numbers, Silver Carp has the potential to cause enormous damage to native species because it feeds on plankton required by larval fish and native mussels (Laird and Page 1996). This species would also be a potential competitor with adults of some native fishes, for instance, gizzard shad, that also rely on plankton for food (Pflieger 1997). A study by Sampson et al. (2009) found that Asian carp (silver and bighead carps) had dietary overlap with gizzard shad and bigmouth buffalo, but not much of one with paddlefish. Asian carps have been shown to affect zooplankton communities (Burke et al. 1986, Lu et al. 2002, Cooke et al 2009; Calkins et al. 2012; Freedman et al. 2012; Sass et al. 2014). Freedman et al. (2012) showed that resource use and trophic levels of the fish community change when Asian carps are present. They also demonstrated an impact on Bigmouth Buffalo and found isotopic values similar to Bluegill, Gizzard Shad, and Emerald Shiner. Irons et al. (2007) showed significant declines in body condition of Gizzard Shad and Bigmouth Buffalo following invasion by Silver and Bighead carps. They state that ultimately, declines in body condition may decrease fecundity. Silver Carp has unique, sponge-like and porous gill rakers capable of straining phytoplankton down to 4 lm in diameter (Robison and Buchanan 1988). They can feed in temperatures as low as 2.5°C (36.5°F) and can withstand low levels of oxygen (Pennsylvania Sea Grant 2015). The Great Lakes contains suitable habitat for silver carp (Chen et al. 2006).

In their native range, Silver Carp reach maturity between 4-8 years old but are noted in North America to mature as early as just 2 years old, and can live to be 20 years old (Higbee et al. 2004). Spawning occurs at temperatures greater than 18°C (Higbee et al. 2004). A mature female can lay up to 5 million eggs per year (Higbee et al. 2004). Eggs require current to stay suspended, with a minimum length of spawning river estimated at 100km and a current speed of 70cm/s (Higbee et al. 2004). Silver Carp require bodies of water with some current for eggs to float and develop properly (Higbee et al. 2004). They prefer to spawn in small groups of 15 to 25 fish at dusk and dawn, at water temperatures of between 18-20°C (Higbee et al. 2004). Typical spawning age can be from 3 to 10 years old (Higbee et al. 2004). For spawning to occur, they require moving water with sufficient current to allow proper egg development (Higbee et al. 2004). Spawning of Silver Carp is similar to Aristichthys nobilis in that it occurs in swift channels of large rivers (Higbee et al. 2004). Flooding of lowland areas is a necessary requirement as these become the nursery areas for larvae and juveniles (Burr et al. 1996).