Fish Reproduction System: How Do Fish Make Babies?

Adult fish basically reproduce in the same way as the higher animals. The female fish produces eggs and the male produce sperm. Egg and sperm combine to produce a new individual, containing genetic material from both parents.

However, the details of fish reproduction are varied. Eggs may be fertilized either externally or internally, depending on species. Also, a few species of marine fish are hermaphrodites, that is, they have both male and female reproductive organs.

The Different Ways In Which Fish Reproduce

Livebearers: Female livebearers are usually larger than the males of the species. The male has a rod-like anal fin called a gonopodium which it uses to deposit sperm into the female. The eggs then become fertilized, and the embryos develop within the female’s body. The young of these fish are “born alive” like those of most mammals.

In ovoviviparous fish, each embryo develops within its own egg. In viviparous fish, however, the embryos obtain the nutrients they require from the mother’s body, not through the materials in the egg.

Examples of livebearers are mollies, platies, swordtails, and guppies.

Egg-layers: These fish are oviparous, this is, they reproduce by external fertilization. A female fish releases eggs into the water to be fertilized by sperm that is concurrently released from a male fish. This process is called spawning.

The embryo in each egg develops and hatches outside the mother’s body. The hatching that emerges then develops by obtaining food from the yolk sac that is still attached to it.

The Different Types of Egg-layers

On Gravel and Plant: Egg scatterers disperse their eggs around plants or onto gravel. The male chases the female during spawning and the eggs become fertilized as they fall. Examples of such fish are tetras, barbs, and danios.

On Substrate: Substrate spawners lay their eggs on substrates like plants, rocks, driftwood and even the glass walls of the tank. Again, the male fertilizes the eggs as the female lays them. Most fish eggs have sticky casings, so they do not float away but adhere to whichever surface they settle on. Examples of substrate spawners are various species of catfish, cichlids and killifish.

Bubble Nest: Male bubble nest builders blow bubbles to form a nest held together with their saliva. A few eggs are laid at a time and carefully place in the nest where they will hatch. The bubble nest keeps the eggs at the surface of the water, where they are kept well-oxygenated. Examples of bubble nest builders are bettas and gouramis.

Mouthbrooding: Mouthbrooders hold their eggs in their mouths until they hatch. A few eggs are laid at a time. Once the male fertilizes the eggs, the parent responsible for mouthbrooding gathers them up in its mouth. That parent eats sparingly, if at all, until the baby fish are released.

In some species, males and females share mouthbrooding responsibilities. Usually, the female will hold the eggs first before passing them to the male. This reduces the stress on the female fish, allows it to resume eating and recover much faster. Examples of mouthbrooders are male arowanans and female cichlids.

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