With crayfish it's an eating world... what does eat them, it will try to eat. So depending on how expensive your fish are.... and since the plecos are bottom feeders, they're be first choice (mind you they'd have best defense, too).
I dont' think crayfish would really work with mbuna, especially if there are catfish and a pleco.Any bottom dweller(or even the mbuna) will get attacked at night while they are sleeping. ANd if the crayfish dont' pick on your fish the fish will most likely try to pick on the crayfish.
I dont' think inverts are best suited to "aggresive tanks". crayfish are best kept in tanks with fish you dont' mind getting eaten or species tanks. Shrimps are peacceful and should be kept with smaller fish taht won't eat them. Snails are your best choice but african are known to pick at the foot of snails, or the breathing tube of some species.Plus some mbuna eat snails.
Clams aren't a good choice, as they dont 'do well in aquariums. And if they die you can't tell and they polute your water.
get another tank and set it up for inverts. I set up my 15g to be a crayfish tank and now that my dearly departed Dr. pinchy has died it mostly contains various shrimp.
hi there
my buddy has a 55 gallon with a dozen or so mbunas, a few tiger barbs and 3 pictus cats- and three crayfish...he has had it set up for about 6 months now- and a few barbs have disappeared- but the cichlids and cats have been untouched... not saying it is safe for every application, but these are pretty big crayfish and he's had no problems.. good luck