Fish aren't "pregnant" by the terms we use for mammals.
Egglayers are never pregnant. They are "gravid" or heavy with eggs. Only thing that ever comes out of them are eggs which may or may not be fertilized by a male.
Livebearers also are never really "pregnant". The eggs are fertilized in the body but unlike mammals they have no connection to the female. They draw all the nutrients they need from the egg sac while a mammal gets it from the mother. So basically the female "broods" the eggs internally. Just about like mouth brooders just a different location in the body.
Technically these fish don't get pregnant as this is a term reserved for the mother providing nutrients during development. Although it would appear to be a pregnancy since the young are born alive it is not. The eggs are developed by the female and then fertilized by the male (or by stored sperm). The fry then develop from the egg without any nutrition from the female other than an oxygen supply. The term used for a female with developing fry is "gravid".