Giant River Prawn

Full-body image


Closeup


In PVC shelter


Climbing up divider


Extending chelae out of the water

One of six species of Macrobrachium found in the continental US (over 200 species worldwide), M. carcinus occurs in coastal streams and rivers from the Gulf Coast to southern Brazil. North America's largest freshwater invertebrates, full grown M. carcinus can exceed 2 feet in length (including the outstretched claws). M. carcinus function as generalist omnivores, consuming a wide range of aquatic plants, annelids, mollusks, arthropods, and fish. In captivity, these prawns take well to pellet and frozen food, though feeder minnows and goldfish are readily accepted. Most tankmates, including conspecifics, are apt to be eaten.

Since all U.S. Macrobrachium require brackish water for larval development (the fertilized eggs are first brooded amongst the swimmerets, or pleopods, much as with crayfish), dam construction puts them all at severe risk. Though many U.S. populations were historically vigorous enough to sustain local fisheries (as they still do in the tropics), M. carcinus appears to have declined considerably along the Gulf. Tragically little is known about even basic life history parameters like lifespan or migratory habits.

In my view, captive breeding and prawn-ladders (ala salmon stairs) hold promise for conservation.

(The shrimp depicted above were collected in northeastern Puerto Rico.)

Source: Bliss, Dorothy E. Shrimps, Lobsters and Crabs: Their Fascinating Life Story (Columbia University Press Morningside Edition, 1990).

Giant shrimp by the numbers:

Within the borders of the United States we have a giant fresh-water shrimp, Macrobrachium carcinus. The largest specimen I have seen weighed three pounds; its body length was ten and a half inches; the feelers, which were missing, were said to have been twenty-six and a half inches long; the larger cheliped of its sturdy pair measured thirteen and a quarter inches. It hailed from the Devil's River, Texas."

Source: Schmitt, Waldo L. Crustaceans (The University of Michigan Press, 1965).

Tragic postscript:

A historic population of M. carcinus reported from the Devils River, a tributary of the Rio Grande (Hedgpeth, 1949), now is apparently extirpated from that system. This extirpation apparently occurred following the erection of Falcon Dam in 1953 on the Rio Grande and Amistad Dam in 1968 on the Devils River near the confluence with the Rio Grande. In recent years, these two reservoirs have yielded minimum flows and have occasionally reached zero flow (Judd, 1995). Proposed reservoir construction on the Guadalupe River near Cuero, Texas, would effectively halt the recruitment of all species of river shrimp above that area, including M. carcinus from Comal Springs and the upper San Marcos River."

Source: Bowles, D.E., Aziz, K., Knight, C.L. (2000). Macrobrachium Bate (Crustacea: Decapoda: Palemonidae) in the contiguous United States: a review of the species and an assessment of threats to their survival. Journal of Crustacean Biology: Vol. 20, No. 1 pp. 158–171

In the 1800s, M. carcinus was the abundant target of a commercial fishery in Texas. By the mid-20th century, these prawns -- though their numbers were evidently reduced -- were crammed into jars for proud display at sporting goods stores and the like all along the Texan coast.

Nice prawns. I have a Macrobrachium sp. thats holding eggs. What salinity do the larvae need?

Ray Bauer spoke at the 2006 MO Convention on these genera. You could almost see him cringe while the Army Corp told us about their progressive river training structures (wing dams) on the Mississippi, as these structures block upstream migration in base flow.

Really cool critters!

Todd

Very nice pics , a few years back we electroshocked quite a few Macrobrachium carcinus (and some fish as well) in canals south of the Miami area in Florida. Apparently they are able to get through the salinity gates that separate these canals from Biscayne Bay. As these gates are completely shut during the dry season (~January to June), they must be moving to and from the estuary during the wet season. Is there any info on when the larvae enter freshwater?

Nice prawns. I have a Macrobrachium sp. thats holding eggs. What salinity do the larvae need?

Congratulations. Do you know where it's from? How large are the eggs?

Some species (no U.S. natives, though) have an abbreviated larval development that takes place entirely in freshwater. For other varieties, I would follow the Macrobrachium rosenbergii model. Since this species is hatchery-bred around the world for human consumption, a great deal of research has gone into larval culturing, and many manuals are available online.

Ray Bauer spoke at the 2006 MO Convention on these genera. You could almost see him cringe while the Army Corp told us about their progressive river training structures (wing dams) on the Mississippi, as these structures block upstream migration in base flow.

Dr. Bauer's doing some great work with M. ohione, a North American endemic that's appears to be making a comeback of sorts in the Mississippi.

Very nice pics , a few years back we electroshocked quite a few Macrobrachium carcinus (and some fish as well) in canals south of the Miami area in Florida. Apparently they are able to get through the salinity gates that separate these canals from Biscayne Bay. As these gates are completely shut during the dry season (~January to June), they must be moving to and from the estuary during the wet season. Is there any info on when the larvae enter freshwater?

Thanks! In natural waters, M. carcinus larvae are released into the current and thereby swept into estuaries, though some females are suspected to migrate downstream beforehand. These larvae seem to require salinities of 14–17.5‰, though they can survive for 2-7 days (conflicting reports) in freshwater.

How large were these canal shrimp? Did they occur alongside lots of alien fish?

It was collected this spring down here in south Louisiana, its body is 3-4 inches long. The eggs are small. I will try and get some pics, but it stays hidden most of the time.

How large were these canal shrimp? Did they occur alongside lots of alien fish?

I don't have length data on them, however some of them were around hand size (not including claws), others were only 2-3 inches long, and a least a few had eggs. The canals had a mix of native and non-native fishes including various Sunfish species, Largemouth Bass, Bowfin, American Eel, Gambusia, Fundulus, Lucania, Armored Catfish, and several Cichlid species.

It was collected this spring down here in south Louisiana, its body is 3-4 inches long. The eggs are small. I will try and get some pics, but it stays hidden most of the time.

Size probably indicates that it was Macrobrachium ohione, which does require brackish water for larval development.