Bloody red shrimp (Hemimysis anomala)

Common Names: red mysid, bloody-red mysid

Description:

Bloody red shrimp (Hemimysis anomala) is a tiny, reddish, shrimp-like crustacean ? a mysid, or "opossum shrimp" ? native to the Black, Azov, and Caspian Sea region of eastern Europe and western Asia [1]. It reached the Great Lakes around 2006, almost certainly in the ballast water of ocean ships, and has since spread through the lakes [1]. MISIN tracks it because it gathers in dense swarms and eats large amounts of the tiny floating animals (zooplankton) that young fish and other water life depend on, which can shift the base of the food web [1][2].

Identification:

Bloody red shrimp is small ? mature animals are only about ? to ? inch long (6?13 mm) ? with large, stalked eyes and a translucent to ivory body marked with red pigment that can make it look blood-red, especially when many gather together [1][2]. Like other mysids, females carry their young in a pouch under the body [1]. Up close, its tail ends in a flat edge with two prominent spines, unlike the deeply forked tail of the native opossum shrimp [1][2]. Its behavior is the easiest clue: it avoids light, so by day it hides near rocky bottoms and under docks, piers, and breakwalls, then forms reddish swarms in shaded water and rises toward the surface at dusk and after dark [2]. These swarms are most noticeable in late summer; shine a flashlight on the water at night and the tiny red shrimp scatter [2].

At-a-glance cues:

1. Tiny reddish shrimp (? to ? inch) with large stalked eyes, often in dense red swarms [1][2]
2. Swarms in shaded nearshore water ? under docks, piers, and breakwalls ? at dusk and night [2]
3. Tail ends in a flat edge with two spines (the native opossum shrimp has a forked tail) [1][2]
4. Swarming behavior unlike anything else in the Great Lakes [2]

Habitat:

Bloody red shrimp lives in nearshore fresh water on rocky or hard bottoms and around man-made structures such as docks, piers, and breakwalls [1][2]. It is usually found at depths of about 20 to 35 feet (6?10 m) but ranges from very shallow water down to about 165 feet (50 m), and it strongly avoids daylight, staying near the bottom by day [1]. It is native to the Ponto-Caspian region ? the freshwater edges of the Black, Azov, and Caspian seas and their large rivers [1]. In North America it has spread through the Great Lakes, including Lakes Ontario, Michigan, Erie, and Huron, with recent records from Lake Superior [1].

Reproduction:

Because it lives in open water, bloody red shrimp spreads through water and the things that move between water bodies ? not across land [1]. It most likely first arrived in ships' ballast water, and it is considered a high risk to spread to inland lakes on boats, in bilge water, live wells, and bait buckets [2][3]. For anyone who boats or fishes, that means it can ride a trailered boat or a bucket of water from one lake to the next. Cleaning, draining, and drying boats and gear between waters is the best way to slow it down [3].

It breeds fast. Females carry their young in a pouch and produce two to four broods a year, with roughly 6 to 70 young per brood, and the shrimp can mature in under 45 days during the warm season [1]. That quick turnover lets dense swarms ? hundreds of shrimp per cubic meter of water ? build quickly once it arrives [1]. There is no practical "remove before it breeds" step for a tiny swimming animal; the realistic lever is keeping it from reaching new waters [3].

Impact and Damage:

Bloody red shrimp poses no danger to people or pets ? it does not bite or sting, and it is simply a tiny water animal [1]. Its impact is ecological, near the base of the food web [1]. It is a hungry omnivore that eats floating zooplankton ? especially water fleas such as Daphnia, along with rotifers and other tiny animals ? as well as algae and detritus [1]. In dense swarms it can reduce the amount and variety of that zooplankton, competing with young fish and other plankton-eaters for the same food [1][2]. At the same time it is itself eaten by larger fish, so its effects cut both ways and the overall outcome in the Great Lakes is still being studied [2]. In Europe, where it also invaded, it has changed zooplankton communities and food webs, which is why it is rated a high-risk invader [1].

Similar species:

Bloody red shrimp is most likely to be confused with other small, shrimp-like crustaceans in the Great Lakes. Its dense red nearshore swarms and its flat, two-spined tail are the best clues.

Opossum shrimp (Mysis diluviana) is the native mysid and the closest look-alike. It is larger, paler, and lives in deep, cold, open water rather than swarming in the shallows, and its tail is deeply forked rather than flat with two spines [1][2].

Scuds (amphipods such as Gammarus and the invasive Chaetogammarus ischnus) are other tiny shrimp-like crustaceans of the same waters. But scuds are flattened from side to side, crawl and hop along the bottom rather than forming red mid-water swarms, and lack the mysid's brood pouch and stalked eyes [1].

Monitoring and rapid response:

Signs to watch for:

1. Dense reddish swarms of tiny shrimp in shaded nearshore water ? under docks, piers, and breakwalls ? in summer [2]
2. Swarms that rise toward the surface at dusk and scatter when you shine a flashlight on the water at night [2]
3. Tiny shrimp with large stalked eyes and a flat, two-spined tail [1][2]
4. Behavior unlike any native Great Lakes animal ? a true mid-water red swarm [2]

What you can do:

1. This is an open-water animal you cannot hand-remove ? the most useful action is stopping its spread between waters [3]
2. Clean, drain, and dry boats, trailers, anchors, live wells, bilges, buckets, and gear before moving from one water body to another [3]
3. Never dump bait buckets, live wells, or aquarium water into a lake, river, or storm drain [3]
4. Take a clear photo and note the exact location if you see a red swarm, since early detection in inland lakes is the most valuable step [3]
5. Lake associations and natural area crews can include this shrimp in nearshore and plankton monitoring, sampling shaded structures at night, and prioritize preventing ballast and bilge transfer between waters [1][3]

When to call a professional:

1. Confirming the species and assessing a population require an aquatic biologist ? it is tiny and easily confused with the native opossum shrimp, so collect a sample rather than relying on a field guess [1][2]
2. Lake- or river-wide management is handled by state natural resources agencies and aquatic invasive species programs [3]
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Hemimysis anomala (bloody red shrimp) ? Species Profile. nas.er.usgs.gov
2. NOAA Great Lakes Environmental Research Laboratory, GLANSIS. Hemimysis anomala (Bloody Red Shrimp). glerl.noaa.gov
3. Minnesota Department of Natural Resources. Bloody red shrimp (Hemimysis anomala). dnr.state.mn.us

---