I'm far from knowledgeable in this area, but will go out on a limb and say that tank maybe too small for even the smallest species of shark... since if i'm not mistaken, most sharks grow to at least 3' in length, so a 4' X 3' will be a tight squeeze and not leave much room for the fish to swim...
Although, with that being said, i would wait for the experts to chime in and give you a solid answer...