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Unique breeding strategies in the fish world

The California grunion found only on the Southern California coast is well-known for its unique springtime spawning behavior. Breeding takes place not in the water, but at extreme high tides on sandy beaches on nights just after the full moon and the new moon between March and August.

During these times, the females ride waves up as far up the beach as they can, dig their tails into the sand, and wait for subsequent waves to bring males to them. Several males wind their bodies around the female and spawn, releasing sperm that flow down the female’s body to fertilize the eggs she lays in the sand, about four inches under the surface. When the process is done, they get washed back to the sea. The buried eggs incubate in the moist sand and usually hatch when agitated by the surf in the next high tide series.

The biggest threat to grunion is human activity: development of spawning grounds, beach grooming using tools that disrupt egg nests, and human harvesting, which disrupts spawning runs.

The Copella arnoldi, a genus of fresh water fish, commonly called the splash tetra, also lays its eggs outside of water. When a male is ready to mate, it takes position in the water below an overhanging leaf. If a female is interested, she will sidle up next to him. Then, they will leap out of the water together. They attach themselves by fin suction to the underside of a leaf, and the female releases six to eight eggs and the male quickly fertilized them before falling back into the water. The pair repeats this process several times until they have deposited about 200 eggs onto the leaf. The male keeps an eye on the eggs. He defends the territory and periodically splashes the eggs with his tail fin to keep them moist.