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Bloody Red Shrimp
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Species at a Glance
The bloody red shrimp is a tiny freshwater crustacean in the order “Mysidacea,” more commonly referred to as mysids. Mysids are also sometimes called opossum shrimp because females typically carry their eggs in a pouch. The impact of this shrimp on the Great Lakes is unknown, but based on its history of invasion across Europe, significant impacts are possible.
Bloody red shrimp are very small; males reach only 8-10 mm (0.3-0.4 in) and females reach 11-16 mm (0.4-0.6 in). They are ivory or translucent, but pigmentation can appear bright red to orange. Their eyes are large, black, and stalked, and they have 8 pairs of legs. A soft carapace covers the head and thorax. Under a microscope, the telson (tail) will be flat with two prominent terminal spikes. While these animals bear live young, juveniles are not easily visible to the naked eye. Its unique swarming behavior is unlikely to be confused with anything else in the Great Lakes. During daylight hours, especially in late summer, it may be observed forming reddish swarms in the shadows of piers, boats, or break walls. At night swarms disperse, but in clear, calm waters, they may be detected by shining a bright light on the water–the shrimp will rapidly swim away from the light.
The native Great Lakes opossum shrimp (Mysis diluviana) also has stalked eyes and overlapping size ranges. The best way to tell these species apart is by the shape of the tail (using a microscope or hand lens). The native opossum shrimp will have a deeply forked tail instead of a distinct flat tail.
This species typically aggregates and hides in rocky crevasses and shadowed areas during the day and disperses to deeper water at night. It typically avoids soft bottoms and vegetation, but can be found in fresh or brackish water over hard bottom surfaces such as rocks and shells.
It was most likely introduced into the Great Lakes through ballast water discharges from transoceanic ships. Inter-basin transfer is most likely facilitated by bait buckets, live wells, bilges, boat motors/trailers/hulls, or other equipment used in the water.
While native to the Ponto-Caspian region of eastern Europe, the bloody red shrimp was first reported in 2006 in Lake Michigan waters. The shrimp’s current distribution includes lakes Michigan, Ontario, and Erie. The closest report to Pennsylvania’s shoreline has been 60 miles north in Dunkirk, New York.
Note: Distribution data for this species may have changed since the publication of Pennsylvania's Field Guide to Aquatic Invasive Species (Second Edition 2015), the source of information for this description.
The bloody red shrimp is considered “high risk" for invasion of inland lakes in the Great Lakes region. Its history of invading canals, streams, lakes, and reservoirs throughout Europe also indicate the potential for significant impacts to our inland lake systems.
Information for this species profile comes from Pennsylvania's Field Guide to Aquatic Invasive Species (Second Edition 2015).