By the "Flipper" comment, I figured he ment a horizontal tail fin, not a vertical. Sorry that came to my mind first, I realize that it is pretty much impossible for you to get a true FW dolphin. I don't advocate live feeding except where necessary (Like gars and such), but not because of cuelty. Feeding you fish live fish is dangerous. They carry diseases and such that could cause a lot of trouble. Getting a bag of frozen "Silversides" might do much better for them. Try some prawns and such to give them a healthier diet with less fat. I'm not exactly sure on the fat content of "Elephant noses" but I'm sure it's pretty high since aquariums fish are often fed on exceedingly nutrisous diets. Be careful not to get too much fat in you Pirahnahs' diet. That too could lead to many problems. Also make sure to remove anything that may be left over (bones and such) and watch for choking on bones and barbs. Good luck and Good fishing!