However, the gestation period could vary from one species to another. Even so, the most common time period is about 4 weeks. This is the time that has to pass from the moment of egg fertilization, to the moment when the birth is taking place.
How do you know when a fish is about to give birth?
The Eyes of the Fry and Signs of Impending Birth
A few days before delivery, she develops a bulge below the gills, her outline becoming fairly square in this region, while the gravid spot has enlarged its area.
How do you know if fishes are mating?
If the female Oscar plays hard to get, the suitor will become more physical with rubbing behavior that may look like fighting when it isn’t. Oscar couples always get along even when they’re not mating, so if you spot aggressive behavior and chasing, you’ll know they’re actually mating.
One explanation for seeing a female guppy fish hanging out at the bottom of the aquarium is that she’s pregnant and in labor. If you’re keeping both female and male guppies, chances are very high that they’ll reproduce and that the female will give birth to fry.