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 the crayfish's large “lobster” claws). Also, the abdomen (“tail”) of shrimp is flattened from side to side, while that of crayfish is flattened from top to bottom.
Of Missouri’s two species of freshwater shrimp, the Ohio shrimp is very much less common. It is translucent pale grayish tan with blackish, brownish, or bluish speckles, and the rostrum (pointed, noselike structure atop the head) has 9–13 sawlike teeth along the top edge, is rounded outward, and has an upcurved, pointed tip.
Similar species: The Mississippi grass shrimp, or glass shrimp (Palaemonetes kadiakensis), is very common. Its rostrum has 6–8 sawlike teeth along the top edge, which is not notably rounded in outline.
Adult length: to about 4 inches (not counting appendages; females much larger than males).
In and along the Mississippi River. It occurs in river systems draining into the Gulf of Mexico and Atlantic Ocean; Missouri is about as far north as it gets. Although named for the Ohio River, it is rarely found in that river anymore.
Habitat and Conservation
Occurs in side channels and main channel borders of the Mississippi River, especially where flooding is occurring. This species formerly migrated from the Gulf of Mexico upstream into the Ohio River, but dams, levees, and wing dikes on our big rivers now prevent it from migrating so far upriver. Pollution also contributed to the decline. The Ohio shrimp was thought to be extirpated from Missouri but was rediscovered, first in 1991, in the Mississippi River along our eastern border.
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 on the surfaces of submerged aquatic plants. The larger plants offer them shelter from predators.
Although its numbers are secure across its overall range within the United States, the Ohio shrimp is a species of conservation concern in Missouri. Here, it is listed as critically imperiled because of its extreme rarity, low populations, and factors making it especially vulnerable to extirpation from our state. We are at the northern boundary of its current range.
Like salmon, the young of this species must grow up in saltwater; when they’re larger they must return upstream to freshwater to reproduce. Human alterations to river flow, like dams, impede their migration and have caused population declines. If, by hatching time, a gravid (egg-laden) female has not traveled downstream to the salty Gulf of Mexico estuaries, then her tiny hatchlings must finish the journey, drifting downstream with the current until they reach salty water. They have only a few days to reach salty water before they die.
Before dams and other flow-control systems were implemented, this species was common in the Ohio and Mississippi river systems, abundant enough that until the 1930s it was sold commercially for people to eat and use as bait. Some Missourians remember stories shared by oldtimers, who told of being able to stick willow branches into the river and pull them out loaded with Ohio shrimp, which could be used as bait. In Louisiana, the Ohio shrimp is still a popular bait for catching catfish.
Other species also move up and down the river, or otherwise need a flowing and open system to complete their life history. The Ohio shrimp functions as an indicator species that biologists use for gauging the health of the Mississippi River over much of its course. Many states and agencies are working together to collect and analyze data for habitat restauration along the river.
Like other migratory animals, this species influences the ecology — eating and being eaten — in all the regions it travels through. It requires healthy wetlands and estuaries along the Gulf of Mexico as well as natural water flow that allows its migrations to occur.