There are a lot of fresh water shrimp in the aquarium trade. I've kept some. Try searching "fresh water shrimp aquarium" or "fresh water shrimp breeding". All the ones I've seen are pretty tiny, so not much use for food. There are however some freshwater prawns that now populate the rivers of Hawaii, I don't remember where they were introduced from. Those could be a food crop, but I thing they need good water quality, making them a bad choice for closed system, high volume aquaculture. That said, fresh water shrimp are expensive and a good income if sold to the aquarium trade. They can also be remarkably beautiful, depending on the species.
I see that you are in Texas. Texas outlawed the raising of fresh water crawfish. As these are from Australia and raised commercially in several states in the US you can find out all that you want to by going to Startpage and in putting "freshwater crawfish". They range in size from smsll shrimp size to several pounds. They are raised in tanks like a lot of different fishes. Good luck and keep your head down.
I'm lucky being an Australian and have them wild in most of our large waterways , as far as aquaponics go they aren't really suited as they need a large amount of floor space to raise a decent number to eat... If you are considering them just for resale into pet trade , or using small numbers to further clean the fish waste they could be worked in rather nicely tho will need some form of segregation for their protection, I found this youtube to show how some aquaponic farmers have gotten around some of the problems with having them http://www.youtube.com/watch?v=lhPfKK6smLA hope this helps Peace and love Dave oxoxox