You can tell if your fish has a reddish or blackish dot near their but. This is called the gravid spot. And you know when they are about to give birth when their bellies square off or start to look...
That depends on the fish (i.e. whether it's an egg layer or a live-bearer). Guppies and swordfish (for instance) develop a dark spot on their lower abdomen which swells as the babies develop. These...
to tell if a guppy is pregnant , look under her stomach . There will be a black dot . This is called a gravid spot . A gravid spot could also be yellow or orange . The guppy will be bigger every day...
We used to have some Mollies, and one of them was actually pregnant. She had a puffed out belly on the bottom, different from the others, and because of that her head was more up.