Jesper
They are imported intentionally, but I should think that at least some are imported with fish. I wouldn't think tropical, as they come from temperate climates...
I would also think that they are caught by accident and then sold on for some extra cash...however there are proper pet trade collection 'missions' - sometimes 1000s of newts are imported at the smae time. Many tropical fish suppliers do deal in newts aswell, so the companies they come from don't always indicate whether they are imported accidentally or not...
I'm not sure why females are so scarce. Perhaps they are more easily captured, or females are less hardy on the way.....who knows. Maybe the males are more sought after cos of 'pretty blue tails'.
Chris