Are Fish Oviparous or Viviparous? A Detailed Explanation of Fish Reproductive Modes

When I was little I remembered that fish were oviparous, but later after keeping fish at home I discovered that they were actually "gifted" live-bearing little fish. So are fish oviparous or viviparous?

Fish reproductive modes are basically divided into three types, namely oviparity, ovoviviparity and viviparity.

1. Oviparity

This is a reproductive mode in which the parent fish directly release mature eggs into the water for fertilization and development. In this mode, the parent fish mostly provide no protection for the eggs they have laid. The eggs are often swallowed in large numbers by various predators, and fertilization and development in the water are greatly affected by environmental conditions; therefore, fish that reproduce by oviparity lay a relatively large number of eggs.

2. Ovoviviparity

This means the eggs are fertilized inside the female fish and develop within the reproductive tract; during development, the nutrients needed by the embryo are, just as in oviparity, supplied entirely by the yolk of the egg itself. This mode is one step more evolved than oviparity, is not affected by a changeable environment, and is more conducive to protecting the offspring. For example, fish such as the sea carp and the mosquito fish.

3. Viviparity

The eggs are fertilized and develop inside the body; during development, the embryo not only nourishes itself with its own yolk, but also produces many folds and protrusions on the wall of the yolk sac that connect with the mother, forming a yolk-sac placenta like an umbilical cord, through which it can directly obtain nutrients from the mother. This reproductive mode is similar to that of mammals and is the most advanced mode, because fertilization and development of the eggs are reliable and guaranteed. For example, the gray star shark (smooth hound shark) and the true shark (requiem shark), etc.