this is a funny excerpt from that thread; appears perhaps its an aussie thing to call pregnant goldfish "twits" and we were taught it in our schools (i was in enzed or godzone at the time lol)
"Now the Australian Going Places magazine claims rather that 'a pregnant goldfish is called a twit.' It has also been suggested that this is a mistaken definition of twat. Confirmation of any of these, please."
I rolled my eyes but dutifully looked up twirp (and twerp) in the OED. No mention of fish, gold or not.
Pursuing the Australia angle, Jill E-mailed a fisheries expert down under, who replied, "I am perhaps not the best to ask about Australian slang (I'm a New Zealander, and for us twit and twerp are names for stupid people). However, I asked my colleagues and it seems that in Australia twit is indeed a name for a pregnant goldfish, as well as having the more normal meaning."
A solid lead or another dead end? Jill knew what to do. She posted a query on a message board run by Australian disciples of the Straight Dope. (They call themselves "the Teeming Handful"--check them out at
http://pub31.ezboard.com/bgdope.) The response: (a) "It's definitely an Aussie [urban legend] that twit stands for a pregnant goldfish. It was one of those 'facts' we all knew at school." (b) It's not in the Macquarie Book of Slang, the definitive work on Australian colloquial speech, or in any other available book of Australian slang. (c) "I've asked my friends who are vets, and it's not a term used by either them or by fish breeders."
So there you have it. You can bullshit the experts all you want. But the Teeming Millions know.