Thanks for all the great suggestions. You people are really creative. I wrote out every suggestion in a note book and we had a lively discussion over dinner as to which it would be. Nicholas was big on "Bam Bam" and "Elmo." Bam Bam is a popular onimonipea with two-year-old boys, I find. And "Elmo" is a reddish puppet that Nicholas has seen on lunch boxes at Walmart.
"George" and "Shark" were pretty popular all around.
We all thought "Mars" was clever, too, being the god of war and the Beta being a fighting fish and all that.
"Zip," "Flash," "Dart," and "Comet" were favorites with Alex, but Simeon objected that the fish mostly just floats quietly in one spot, for which reason "Racecar" was also out of the running. Alex agreed, but counter objected that the fish does "Dart" for food-- at which point I suggested we name him "Glutton."
We couldn't use "Finny" because that's what Zachary used to call Simeon back when he pronounced his S's like Fs and his Ms like Ns. Simeon became Fineon, or "Fini" for short. Zachary laughed at himself when I explained this to him. Now that he's all grown up, wearing 3T clothes and Bob the Builder underwear he can hardly believe he ever made such silly mistakes.
"Bubbles" was out of the question because they have a cousin named "Bubbles"... or at least that what she told us her name was when we asked her once recently and it sort of stuck with the boys.
I just loved "Radius," but the cleverness of it was lost on my children.
"Pirate" was also popular and I tried to get them to accept "Indigo" in lieu of "Purply" and it very nearly worked, but everything lost out to the ever popular "Rainbow."
Thanks, Barbara, for a great name. I guess you are a better namer than you thought.