i have a 400 gallon tank and it has one large freshwater prawn in it but i want to add a cichlid but i don't want anyone which will turn into prawn food.The prawn is 8 inches long.
Wow, tricky... I guess it depends on how fast he is and what times your prawn is active. If he's diurnal (active in the day) I wouldn't worry about anything. If he's nocturnal, he might kill a sleeping fish. I've heard of this happenening numerous times with smaller fish. Second, what are your water parameters and how much do you know about cichlids? If the prawn is diurnal and is in soft, acidic water, I'd recommend 4 or so oscars. They're aggresive, bulldozey fish and should be ok with your prawn if the above conditions are met. If he's in harder, alkaline water, how about some quick-moving, aggresive Africans, like Mbunas?