Not really a true deffinition of 'pregnant' is it?
A hen lays eggs every day, whether they are furtile or not.
Our fish have layed eggs which weren't fertile, we as humans 'lay' an egg every month, but we are not pregnant.
Though we are being a little picky, the fact is that a fish of any kind, whether with or without eggs is not called a twit.
tr.v. twit·ted, twit·ting, twits
To taunt, ridicule, or tease, especially for embarrassing mistakes or faults. See Synonyms at ridicule.
1. The act or an instance of twitting.
2. A reproach, gibe, or taunt.
3. Slang A foolishly annoying person.
[Short for obsolete atwite, from Middle English atwiten, from Old English ætwtan : æt, at; see at1 + wtan, to reproach; see weid- in Indo-European roots.]