The Grass Carp (Ctenopharyngodon idella) is a large minnow species native to Southeast Asia and China. They are an invasive species in parts of the US where they have been introduced as aquatic weed control, and have subsequently escaped. They are unique in that not all individuals are problematic, as sterile, triploid Grass Carp are frequently used as effective weed management.
The Grass Carp has a widespread distribution, having been reported in roughly 45 states (Nico and Maynard et al. 2018).
Grass Carp are a morphologically unique fish in the US, readily identifiable using a few highly noticeable characteristics. These include an overall drab green/olive color, extremely large scales, a terminal mouth with large, somewhat fleshy lips, lack of barbels, and the short, triangular dorsal fin located centrally, almost directly above the pelvic fins. Their size is also distinctive, as they tend to be about 49 inches(125 cm) (Nico and Maynard et al. 2018).
The enormous scales are one of the Grass Carp’s most defining features.
Note the fleshy appearance of the lips and the lack of teeth, which is the result of the Grass Carp’s status as an herbivore. Lack of barbels is another distinctive characteristic of this species.
A white belly is another feature of Ctenopharyngodon idella.
Grass Carp are voracious herbivores, capable of destroying all aquatic vegetation in a given waterbody. The images above show the channel at the base of the Bonnet Carre Spillway control structure. While some terrestrial vegetation is inundated due to high river stages, the channel at normal level is devoid of plant life, likely due to Grass Carp that have become trapped.
Grass Carp are problematic in places where large river systems allow them to reproduce and spread. Their reproductive biology dictates that they can only spawn in the backwaters of large rivers on a rising stage. Pictured is the Bonnet Carre Spillway, an overflow of the Mississippi River - home to a well-known Grass Carp population.
No true biological control exists for Grass Carp, at least not beyond the predatory capabilities of native fish, most of which Grass Carp will outgrow. The only truly effective method is human harvest: angling, bowfishing, netting, treble hook snagging, etc. Grass Carp make surprisingly good table fare, and can also be used as agricultural/garden fertilizer.
Because traditional angling for them can be quite difficult, alternative methods have gained popularity. These images show treble hook snagging in the Bonnet Carre Spillway.
This is a large Grass Carp (40 lbs.) captured in the Bonnet Carre Spillway in April 2018. A fish this size can devastate the aquatic vegetation in a waterbody. The fact that this fish was captured in the Lower Mississippi River near Norco, LA highlights the biggest current concern with Grass Carp - that they will escape into the fragile marshes surrounding the Mississippi Delta.
Nico, L., E. Maynard, P.J. Schofield, M. Cannister, J. Larson, A. Fusaro, and M. Neilson. 2018. Cyprinus carpio. USGS. https://nas.er.usgs.gov/queries/factsheet.aspx?speciesID=4. (Accessed 21 April 2018).
Nico, L.G., P.L. Fuller, P.J. Schofield, M.E. Neilson, A.J. Benson, and J. Li. 2018. Ctenopharyngodon idella. USGS. https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=514. (Accessed on 19 April 2018).
Authors: Christopher Geisler, and Catherine Barry.
Instructor: Dr. Rodrigo Diaz, firstname.lastname@example.org