C.N.
I have to disagree about goldfish having no personality and all looking alike. My daughter came home from a fair with a goldfish in a baggie that she won tossing softballs at milk bottles. That fish was SMART. My daughter trained her to take food flakes out of her fingers.She would actually jump out of the water like a little orange dolphin. She liked to be talked to, and would ram the side of the tank if you passed her without speaking. You could hear her tiny mouth bones clinking on the glass. We had her for seven years, and all cried for days when she died.
Tell the child the truth, and help her deal with her grief. Death is an inescapable part of life.