Gulf State Residents - Please Read

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Cuvier

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Feb 26, 2006
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I'm seeking a good number of juvenile to adult Macrobrachium spp. (river prawns). These are not regular grass/ghost shrimp (Palaemonetes spp.), though it may be hard to distinguish very young specimens.

The genus Macrobrachium, or river shrimps, is represented in the United States by 6 species: M. acanthurus, M. carcinus, M. faustinum, M. heterochirus, M. ohione, and M. olfersii. River shrimps are the largest fresh-water crustaceans in North America, and specimens of the largest species, M. carcinus, can be the size of lobsters. Most of these species are distributed among the southern states of the Gulf Coastal Plain, Mexico, and the Caribbean Islands. Macrobrachium ohione is known also from the Red River drainage in Arkansas and Oklahoma, and the Mississippi River-Ohio River drainage in Illinois, Indiana, and Ohio.
Click to expand...

(http://apt.allenpress.com/aptonline/?reque...ue=01&page=0158)

Prioritization:
  • While I won't go so far as to turn down any of the listed species, I will list them in decreasing order of preference : M. carcinus, M. heterochirus, M. ohione, M. olfersii, M. faustinum, M. acanthurus, M. rosenbergii.
 
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Visual Key:
 
Where to find them:
  • All of these species require saline water (brackish to full marine) for larval development. In many cases, adults must migrate to estuaries or lower stream reaches in order to breed or release planktonic zoae. Therefore, they will not be found in abundance upstream of major impediments to two-way movement (e.g., dams). For this reason, some populations may be limited to coastal regions.
  • Primary habitat: rivers, slow creeks, stream pools, springs, and lakes.
  • Examine overhanging banks, masses of vegetation, and the undersides of submerged logs and stones.
Capture:
  • Long-handled dipnets, seines, and crayfish/shrimp traps (baited with any sort of meaty substance) may be employed (this page provides a fairly detailed overview). Small traps, however, will exclude adult M. carcinus.
  • Willow sets lodged into promising stream banks will serve as attractants (after several days, carefully shake them out on the shore).
  • Less versatile alternatives (mostly suited to crevices) include fishing rods (see http://www.tackletour.com/reviewshrimptw.html & http://www.interq.or.jp/ox/atn/tenaga.html) and nooses.
  • In tight situations, improvised bait-on-string arrangements may be worth a shot, but I'm unsure whether Macrobrachium spp. will "latch on" to food items in the manner of blue crabs and crayfish.
Misc. Collection/Housing Notes:
  • River prawns, especially where predatory fish are present, tend to be nocturnal. Dusk and dawn are opportune times to observe them in the open. Alternatively, headlamps or flashlights may be employed – eyeshine (usually white or reddish) gives them away. Example: http://www.churaumi.net/eco/nature/tenagaebi.jpg.
  • Adequate oxygenation is at all times vital.
  • Cannibalism may prove problematic; house prawns as individually as possible. Do not mix large adults or disparately-sized individuals.
  • River prawns are thigmotactic: provide specimens of all sizes with material to cling to during transport (e.g., aquatic plants). Avoid bare tanks.
  • Insufficiently thin shipping bags may be punctured in transit by large specimens.
  • Persistent, abnormal opaqueness of tissue (for juveniles and normally translucent varieties) usually indicates moribund status.
  • Keep in mind the fact that copper-based aquarium medications and prophylactics are invariably fatal to shrimp
Species Guide:
  • Crayfish or shrimp?
  • At a glance, Palaemonid shrimp are immediately distinguishable from crayfish insofar as much that the second pair of legs (as opposed to the first) are modified into chelipeds ("claws").

    Grass shrimp
  • (Palaemonetes) are usually 25 to 45 mm long; anything larger is almost certainly a Macrobrachium of some sort.

    River prawns
  • Macrobrachium carcinus: painted river prawn, bigclaw river prawn, giant river prawn: rivers, spring brooks, and springs. Primarily found in (but not restricted to) Florida, Texas, and Louisiana. M. carcinus is the largest species found in North America (to 600 mm total length) and is most easily recognized by the short carpus and a single triangular "tooth" on each of the fingers of the chelipeds. The body of this species often has a green tint, and the chelipeds are usually green with orange articulations. More info at http://www.fs.fed.us/r8/caribbean/wildlife...ober-2003.shtml
  • Macrobrachium heterochirus: (No English common name): continental U.S. presence doubtful – perhaps in Florida or Texas
  • Macrobrachium ohione: Ohio River shrimp, stump shrimp: North Carolina, South Carolina, Georgia, Alabama, Mississippi, Arkansas, Louisiana, Ohio, Illinois, Missouri, Indiana, Oklahoma, and Texas. Up to 95 mm: this is the only species in North America in which the females grow larger than the males. M. ohione is characterized by slender chelipeds which are about the same length as the body. They are generally pale gray with small blue spots freckled on the body. M. ohione is the only Macrobrachium sp. endemic to North America.
  • Macrobrachium faustinum: (No specific common name): Possibly Florida. 50-70 mm without claws. See http://www.petshrimp.com/macrobrachiumfaustinum.html.
  • Macrobrachium acanthurus: cinnamon river shrimp: Georgia southwards. Body up to 95 mm long; chelipeds as long or longer. M. acanthurus is similar in color with a brown to green body; however, the edges of the abdominal pleura and uropods shade to red. It also has a distinct brownish orange stripe extending along the dorsal surface of the abdomen. Other distinguishing features include a long, slender, cylindrical carpus and chela, and fingers covered with fine setae.

    Introduced Macrobrachium
  • Macrobrachium olfersii: bristled river prawn: Florida, Missisippi, Texas, Louisiana. Males to 90 mm, females to 65 mm. See http://nis.gsmfc.org/nis_factsheet.php?toc_id=142.
  • M. rosenbergii, Malaysian giant river prawn: Hawaii and the Southeastern U.S. To 600 mm. Sub-adults may appear similar to M. acanthurus or M. ohione.
  • Indeterminate Macrobrachium sp.: western Montana, likely in geothermally-heated waters (consult map).
 
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