I have been keeping a M. carcinus male for about 7 months now without any problems. I caught him when he was about an inch long and more of a glass shrimp than anything. I had no idea that he'd turn out to be a huge Macrobrachium carcinus. He's about 4-5 inches now *without* the claws, so he's technically just a young adult or old juvenile. I don't keep him any differently from my other Macros, except that he is now by himself as he will attack and eat everything else in his tank, including females of the same species.
Until about two months ago he was in a 55 gallon, but I am utilizing that tank for other purposes now....so he is, for now, in a 10 gallon with a large sponge filter attached to a powerhead. He has become more of a pet than anything as he has become very tame. During feeding time he dashes to the front of the tank waiting for his food. He even sticks his *huge* claws out of the water in expectation.
I don't see any problems at all with restlessness, even in the 10 gallon tank, which is way too small in the long run of course. (Hence I do NOT recommend this for any large Macro) I have to do 50% water changes a few times a week to keep up with the nitrate increases in that tank as he eats tons and tons of food. He eats pretty much anything...the main diet is fish food, but the bottom of the tank is covered with leaf litter. He chomps down on the leaf litter litter, as do all my other Macros. He was also eating the Najas when I still had some in the tank.
I think many researchers have trouble keeping shrimp alive in captive setups over the long run because that's not usually what they are trained to do. Most of them are best at catching the animals and immediately transferring them into a container filled with 70% alcohol or another preservative.
It takes some experience keeping shrimp happy in captive setups, especially large and/or sensitive shrimp...more experience than you would need with most fish species.
So, I really think that the researchers you talked to are mistaken in this case. M. carcinus can be kept without problems in captivity given enough space. However, I do not necessarily recommend keeping it, as it is *the* most aggressive shrimp I have ever seen. I only have it because I was catching cave macros and the scientific literature said that there are only cave macros (Macrobrachium lucifugum) in that cave. It turns out they were wrong. I did not know I had a M. carcinus at that time as it was still a juvenile. I also caught what turned out to be Macrobrachium crenulatum from that same cave. See? Another example where scientists are simply wrong.
