Oviparous animals with no gestation period?

Answer 1

There are many fish and amphibians for which the female lays soft-shelled unfertilized eggs, which the male then fertilizes. Because the fertilized eggs were never inside the female's body, one might say that there was no gestation period. However, all animals that have internal fertilization have some length of gestation period. For most animals, the gestation period is much shorter than the time between laying the eggs and the eggs hatching: for example, a chicken egg has a gestation period of one day, but the eggs do not hatch until 24 days after being laid. Monotreme mammals (platypuses and echidnas) have longer gestation periods and proportionally shorter distances between the laying of the eggs and the eggs hatching.