How Do Saltwater Fish Mate?

Mating Season

Mating occurs at different times for different types of salt water fish. Seasonal cues such as light and temperature trigger mating in some species so that it occurs just in the summer months. Other breeds of marine fish mate once a month regardless of the seasons, usually either at the full moon or the new moon. The Butterflyfish is an example of a species that migrate prior to mating to ensure the young are born into an environment rich in food and where the temperature is warmer, giving their young a better chance of surviving into adulthood.

Some breeds form monogamous pairs, often times choosing a mate while the fish are still in their juvenile state. Other species will mate in large groups, or schools. Some fish, like the Midnight Angel Fish breed in harems. In this case one male has four females who display a specific hierarchy. If something happens to remove the male from his harem the highest ranking female will turn into a male over the span of a few weeks.

Preparing to Mate

Many types of fish simply release their eggs into the water. Others prepare a site to deposit the eggs in advance, such as building a nest in the sand or cleaning off of rocks where the eggs will stick until they hatch.

Courtship Displays

Many marine fish perform courtship displays. The Angelfish, for example, have a 'soaring' display where the male will float above the female with all his fins outstretched. More frequently the males will circle a female several times prior to mating. Courtship can last from a few minutes to an entire day prior to mating.

Spawning

There are two biological strategies for salt water fish to produce their young. With the Oviparous type of fish the eggs are fertilized outside the female's body. She lays her eggs and the male covers them with his sperm. Viviparous fish have internal fertilization. These fish mate in pairs and the female gives birth to live young. Either way hundreds to thousands of eggs or live young can be produced.

During mating the male and female usually nuzzle close to each other. The release of the eggs and sperm often happen simultaneously. This often occurs at twilight when the eggs will be less visible to predators.

Post Mating Behavior

Some types of fish will engage in a brief chase after mating. It is suggested that this is done to prevent the parents from eating their young. With other species the eggs are protected in a nest built in sand, gravel or debris. In many species of salt water fish it is the males that are responsible for the protection of their young. The clown fish is an example.

Birth

Newly born fish are called fry. With some species of fish the eggs hatch in as little as 18 to 30 hours. They often have an attached yoke sack to help them to continue to grow. Other types of fish take a few days to hatch. Fry feed on plankton and tend to mature quickly. Most fry are eaten by predators and do not reach adulthood.