By Shikha Singh, PhD
Grass carp is a fish species with a voracious appetite for aquatic plants, and can eat up to 40 % of their body weight per day! Highlighting one of the reasons why this species was introduced to the United States from Taiwan and Malaysia, to control aquatic weeds.
Asian carp are a group of four species of fish that include Bighead, Silver, Black and Grass carp. Common features of all of these fish include they are fast growing, have a big appetite, can get large, and eat plankton. A lot of attention and media coverage has been on the Bighead and Silver carp as they have been slowly moving towards the Great Lakes via the Mississippi River, and there is concern that they will breach the various barriers and decimate the Great Lakes fisheries by out competing the native species for food and habitat. Popular videos show them jumping behind motor boats and hitting boaters. To add insult to injury, it seems that the invasive Eurasian watermilfoil plant is not a species preferred by carp, so they are not likely to help control aquatic invasive plants. Of the above species, Grass carp is already here.
Anglers have reported catching Grass carp for the past 40 years, however, they were thought to be sterile carp which thought to have escaped various ponds or stocked lakes (where they were brought in to control weeds). Legally introduced Grass carp were tested for sterility prior to being introduced, as posted by the National Park Service (NPS) website. Because Grass carp eggs require high flow, oxygen rich water for reproductive success (eggs will not be successful in hatching if they sink to the bottom), it was hoped that if spawning Grass carp were in the region, this limiting factor would keep them from being a problem. However, in 2015, researchers collected eggs and confirmed that Grass carp were naturally spawning within the Great Lakes tributary (Embke et. al. 2016), and sampling efforts by USGS/Dr. Christine Mayer's group found larval Grass Carp in the Maumee River (confirmed via genetic sequencing).
These recent findings are concerning, and hopefully will propel Grass carp into the limelight as a species to keep an eye out for, alongside the Bighead and Silver. This also highlights the need for anglers and commercial fishermen to inspect their catch for Grass carp and report sightings to State officials and/or the local CISMA. To prevent the spread of Grass carp, make sure you know what species are in your bait bucket as juvenile carp do look similar to other fish such as Alewife and Shiners. This caution also extends to bait bought at large retail stores. Do not dump unused bait back into the lake/river, dispose of in the trash. To see a detailed guide to what juvenile carp and Alewife/Shiners look like, please click here to access the MDNR brochure.
For More Information:
Embke, H.S. et al. 2016. First direct confirmation of grass carp spawning in a Great Lakes tributary. J. Great Lakes Research. 42(4): 299-903
MDNR. 2019. Asian Carp: Know the Facts and Learn How You Can Help.
NPS. 2019. Grass Carp. Date Accessed: 3/12/2019. https://www.nps.gov/miss/learn/nature/ascarp_grass.htm
USGS. 2019. Newly Hatched Invasive Grass Carp Found in Maumee River, Ohio.
Shikha Singh is the coordinator for the JLW CISMA. She has a BSc. in Biology from University of Western Ontario, and her master's and PhD at Michigan State University from the Dept. of Fisheries and Wildlife. Her areas of expertise include water quality, water policy, invasive species, education/outreach and public speaking.