I second the Tilapia motion. The reason i say this is because i see them all the time at a Vietnamese Restaurant that i go to on weekends lol. They have about 15 large ones in a tank and I guess they just take them out and fry them to order.
yes they are very active.. i googled them and clicked on images these guys can get huge. one picture showed a person holding one with 2 hands and it was dwarfing him. but i couldnt get another name besides tilapia
before even scrolling to the other replies my thoughts were tilapia too. Im just curious as to what kind considering they have no marking at all and are pure silver, im not good with tilapia id.