Pyramid_Party;2548086; said:
All the species of prawn in this thread live in freshwater as adults and juveniles, but their larval stages (plankton, essentially) require saline water to develop. The average hobbyist, in other words, can keep them in full freshwater, but would have to go to some trouble to breed them. Which is not to say that trying to do so wouldn't be worth it ... each female bears many thousands of young.
M. rosenbergii (Malaysian prawn, giant river prawn, blue prawn, etc.) is the easiest to find ... I've seen 4-5 inch specimens at Petco for a reasonable price. The others are extremely hard to come across in the hobby ... lack of aquarist interest/awareness plays a role. The M. carcinus shown crawling on tank dividers on the first page of this thread were collected in Puerto Rico.
A much smaller species of Macrobrachium able to complete its life cycle in freshwater is readily available, however -- look into redclaw shrimp, M. assamense or dayanum complex (taxonomy's a bit of a mess).
You'll occasionally also find juvenile Macrobrachium as contaminants in shipments of ghost shrimp or various algae-eating shrimp.
