Freshwater shrimp are similar to crayfish but are easily distinguished from them. First, they are slender and nearly transparent. Shrimp have only the first 2 pairs of legs with pincers, whereas crayfish have pincers on the first 3 pairs of legs (the first pair being large “lobster” claws). Also, the abdomen (“tail”) of shrimp is flattened side to side, while that of crayfish is flattened top to bottom.
Of Missouri’s two species of freshwater shrimp, the Mississippi grass shrimp is by far the most common and widespread. The rostrum atop the head has 6–8 sawlike teeth along the top edge, which is not notably rounded in outline.
Similar species: The Ohio shrimp (Macrobrachium ohione) was recently rediscovered in the Mississippi River. It is translucent pale grayish tan with blackish, brownish, or bluish speckles, and the rostrum atop the head has 9–13 sawlike teeth, is rounded outward, and has an upcurved, pointed tip.
Adult length: to about 2 inches (not counting appendages).
This species occurs in Missouri’s eastern counties along the Mississippi River and in the Bootheel. Its broader range extends along the Great Lakes from Minnesota, Michigan, and New York south along the Mississippi and Ohio rivers to states all along the Gulf Coast, from Texas to Florida.
Habitat and Conservation
In Missouri, this very common freshwater shrimp lives among aquatic vegetation in the shallows and backwaters of slow-moving lowland streams and in pools and swampy areas.
These delicate crustaceans feed on a variety of very small invertebrates, plankton, and algae, and on various kinds of organic detritus. They often eat algae and other small organisms that grow upon the surfaces of submerged aquatic plants. The larger plants offer them shelter from predators.
Females carry their eggs attached to swimmerets beneath the abdomen. When the young hatch, the earliest stages are planktonic, drifting around in the water at the mercy of currents, not walking on the bottom substrate. These larvae are called nauplii (pronounced NOP-lee-eye; singular, nauplius), and they look very different than the adults; they have only 3 pairs of appendages. As they eat, grow, and molt, they acquire different forms, finally taking on the form and lifestyle of adults. Most live no more than a year.
Freshwater shrimp are not eaten by people and are not important as bait. However, the freshwater “ghost shrimp” commonly sold at pet stores are usually some species of Palaemonetes, and therefore closely related. You might also have heard of cleaner shrimp, which are in the same family; they are popular in marine aquariums.
Freshwater shrimp are a favorite prey of fish and other animals. They are important in estuary habitats, transferring food energy from the simple plants and decaying plants and animals they eat, to the carnivores that eat them. Researchers use freshwater shrimp as indicators for evaluating pollutants in a body of water.