Bloody red shrimps are small animals that look like miniature shrimps. Adults range from one-fourth to one-half inches in size and are translucent to yellow-white in body color with red spots of pigment. It looks similar to the native opossum shrimp (Mysis diluviana), but can be identified by the red pigment spots and the shape of the telson (tail end of the abdomen). However, under some conditions the pigmented spots may be indistinct. Its small size and similarity to the native opossum shrimp make this a difficult animal for non-specialists to conclusively identify.
The bloody red shrimp is a crustacean, belonging to the same group as the much larger crayfish. It eats microscopic animal life called zooplankton such as Daphnia, but may also eat algae, tiny aquatic insects and organic matter. It prefers warmer water temperatures (50 – 70° F) and can have two to four broods in the summer, with up to 70 young in a brood. High densities of bloody red shrimp are possible in lakes and rivers. They avoid bright light, commonly staying near the bottom of the water during the day and ascending at night to feed. They may be seen as reddish-colored ”swarms” near structures such as breakwaters and piers.
Origin and spread
The bloody red shrimp is native to Europe and Asia. The species was unintentionally introduced into the United States’ Great Lakes through the discharge of contaminated cargo ship ballast water. It has spread throughout most of the lower Great Lakes as well as some inland canals and lakes in New York. The first confirmation in Minnesota was in Lake Superior’s Duluth harbor in 2018. The discovery was a single specimen at a single sampling point and is the only discovery so far in Minnesota waters.
Don't be fooled by these look-alikes
They can look similar to the opossum shrimp (Mysis diluviana) which can be found in scattered lakes primarily in northern Minnesota. The opossum shrimp has a forked telson (tail end of the abdomen) whereas the bloody red shrimp has a truncated telson.
The bloody red shrimp is an unlisted invasive species in Minnesota. Unlisted nonnative species are those that are not prohibited, regulated, or unregulated. Several steps must occur before an unlisted nonnative species may be legally released into a free-living state:
- The person proposing to release the species must file an application and supporting information with the Minnesota DNR.
- The DNR must conduct a thorough evaluation.
- The species must be designated into an appropriate classification.
Threat to Minnesota waters
Invasive species cause recreational, economic and ecological damage—changing how residents and visitors use and enjoy Minnesota waters. Since the bloody red shrimp has not established populations in many inland lakes, there is little information about its impacts to smaller lake systems. Therefore, the threat extent to Minnesota waters is currently unknown.
Potential bloody red shrimp impacts may include:
- Preying on native zooplankton, including Daphnia, which are an important food source for native fishes, potentially impacting aquatic food webs.
- Changing the kinds and abundance of algae in a lake.
- Providing a food source to some fish.
What you should do
People may spread bloody red shrimp primarily through movement of water such as in bait buckets, live wells or bilge areas.
Whether or not a lake is listed as infested, Minnesota law requires water recreationists to:
- Clean watercraft of all aquatic plants and prohibited invasive species.
- Drain all water by removing drain plugs and keeping them out during transport.
- Dispose of unwanted bait in the trash.
- Dry docks, lifts, swim rafts and other equipment for at least 21 days before placing equipment into another water body.
There is no known effective population control for bloody red shrimp in natural water bodies at this time.