The Frog Blog – Fish Friday
Welcome to Friday everyone! Today we will be looking at a fish that has a lot of aquatic weed management potential and may already be in many of your ponds, the grass carp or white amur (Ctenopharyngodon Idella).
Grass carp are actually a non-native fish species introduced to the United States from Eurasia around the 1960s. They are actually a member of the minnow family (Cyprinidae) which is surprising given the fact that they can grow to massive sizes. They are fairly easy to identify with a relatively large, smooth looking head compared to its body, which has an almost scaly appearance. Some may mistake the common carp (Cyprinus carpio) for the grass carp but can be separated by their dorsal fins. Common carp have a long connected dorsal fin that is much longer than that of the grass carp. Additionally, grass carp lack barbels near its mouth, a trait that some other large minnow species have.
Grass carp are highly debated as a useful management technique for aquatic vegetation in small ponds. As a herbivore, they can consume large, almost unbelievable quantities of vegetation. This is why many people stock them. The idea is that a correct number of grass carp will reduce vegetation enough to minimize nuisance plants impact on the pond’s use. This can be true in some situations but some information should be collected on your pond before you decide to stock them or risk causing more harm than good. First, weed identification is extremely important since grass carp can be picky eaters (e.g. they don’t like to eat Eurasian watermilfoil). This can lead to native, beneficial vegetation being consumed over nuisance growth. Secondly, understanding stocking rates relative to your pond size is also important since way too many grass carp will decimate all plants in your pond. This may lead to an algae dominated pond. Finally, you need to ensure the carp you are purchasing are triploid rather than diploid. This will stop these non-native fishes from reproducing and potentially becoming invasive. If all of these factors are looked into, then grass carp may be a potential contender for management in your pond.
by: Ed Kwietniewski
Aquatic Biologist
AQUA DOC Lake & Pond Management
External Sources:
Freshwater Farms of Ohio. (2015). “What is the Difference Between White Amur and Grass Carp?” Accessed March 9, 2018. https://fwfarms.com/author/dave/
Nico, L.G., P.L. Fuller, P.J. Schofield, M.E. Neilson, A.J. Benson, and J. Li, 2018, Ctenopharyngodon idella (Valenciennes in Cuvier and Valenciennes, 1844): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=514, Revision Date: 2/2/2016, Peer Review Date: 4/1/2016, Access Date: 3/9/2018