Bull sharks are one of he sharks that can be kept in freshwater, however, they need to be of one of the strains from lake nicaruaga. The sharks that are indeginous to the us, such as the ones that are from my area, are not really able to stick with freshwater their whole lives. They also get right grumpy when in freshwater. Also, you have to consider the full size of 8' of this species. I have caught them up to that size, so they do get tht big. For a requiem shark, you need at least 8x the length of the body in length of the aquarium, plus 3x for the width. That means that the tank would need to be at least 64' long by 24' wide. At the minimum. If you want to keep sharks, may I suggest one of the bamboo sharks, alot less manageable for their adult size.