There are different stages of a young fish’s life. They are referred to by many names throughout the first years of their survival. Depending on the species will determine what stages and names a baby fish are referenced by. This can include egg, yolk-sac larvae, fry, and juvenile before reaching maturity.
There are three ways for a fish to reproduce. This is either through livebearing, which is similar to the way humans and other mammals produce their young, spawning, or self-bearing.
Spawning is the process when the female fish releases her eggs. The eggs are either deposited directly into the water, where they float around, or into a nest. This depends on the type of fish species. The male fish will then fertilize the eggs with milt that they release. Not all eggs that are laid will be fertilized. Depending on the species of fish, the fish will spawn every year, every four years or only once in their lifetime before dying.
Some fish can switch genders. This allows them to complete the entire process of reproduction themselves. This process is also known as self-bearing.
Fertilized eggs hatch in two to eight days, depending on the species of fish. The majority of eggs don’t reach maturity due to the different threats they face. Some of these threats include the change in water temperature that can occur due to the changing seasons during spawning. Oxygen levels changing in the water is another common threat to fertilized fish eggs. Flooding and sedimentation that carry the eggs to unhealthy areas or cause them to become landlocked will prevent the egg from hatching. Predators and disease are a constant threat to fish at all stages of their lifecycle.
The larvae stage for a baby fish begins nine to 18 days after the egg has hatched. This is also called the yolk-sac phase as the yolk-sac stays attached to the baby fish once it is hatched. This yolk-sac provides the young fish with the nutrients it needs to grow within its environment. Some species of fish, such as the catfish, do not go through this stage.
The larvae stage of the baby fish’s life lasts one to two weeks. During this time, it feeds off the yolk-sac while staying at the bottom of the water. When in the larvae stage, many species of fish tend to settle within the plants and other caverns at the bottom of the water for protection. This helps them blend in and hide from predators as they don’t have fins for swimming and are classified as free floaters.
As a fry, a young fish still has its yolk-sac attached, but it begins to diminish in size. The fry stage lasts for two to five days for most types of fish. The fry will stay at the bottom of the water during this time. However, it does begin to explore its new surroundings, coming out of hiding for short periods of time. Most of a fry’s nutrition comes from the remaining yolk-sac, but it will begin feeding on food lying at the bottom of the water’s bed.
As with each stage of a fish’s life cycle, the amount of time the baby fish remains a juvenile depends on its species. This stage may last up to three years. The juvenile fish begins to develop its fins, and their gills mature throughout this stage. Juvenile fish are not able to reproduce. The beginning of the juvenile stage is crucial to the fish’s survival, as it must learn how to survive among its predators, find enough food to survive and gain its independence in all other aspects.