Prior to the onset of breeding, males will develop a reproductive phenotype, including blue eyes, red throats, and red fore-bellies. During the breeding season, a male will leave the shoal and settle on the bottom in shallow water, where he will construct a nest and establish a territory. The males are are generally not monogamous, and a male often tries to lead numerous females into his nest to lay eggs. Afterward, he will fertilize all the eggs at once.
Males attract females with zig-zag-like courtship dances, and females respond with a form of dancing, as well as a "head-up" posture. The male will then lead the female to his nest, lying on the substrate next to the entrance to signify that she may enter and lay her eggs. Females lay their eggs in the male’s nest and then leave the male alone to attend to the eggs until they hatch. Once eggs are fertilized, they may take five to ten days to hatch, depending on the temperature of the water. The male nesting cycle consists of a sexual phase for 1 to 4 days, and then a parental phase after the eggs are fertilized.
Mating System: polygynous
Threespine sticklebacks breed in sloughs, ponds, rivers, lakes, drainage canals, marshes, tidal creeks and sublittoral zones of the sea. Individuals reach sexual maturity at between 1 and 2 years of age, and breeding occurs annually from late April to July.
Breeding interval: Threespine stickleback generally breed once yearly
Breeding season: late April to July
Range gestation period: 5 to 10 days.
Average time to independence: 2 weeks.
Range age at sexual or reproductive maturity (female): 1 to 2 years.
Range age at sexual or reproductive maturity (male): 1 to 2 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
Once males shift to their parental phase, they provide all the care for their young. This includes fanning eggs with their pectoral fins to provide oxygen for the developing embryos and protecting them from predators. They also convert the nest into a nest pit, which consists of tangled vegetation where newly hatched fry can hide and rest. The males typically defend the fry up to two weeks after hatching. Paternal care has been identified as an important social factor in threespine stickleback development and learning. Sticklebacks with no paternal contact tend to fail avoiding predators later in life. These anti-predator behaviors may be stimulated at an early age as stickleback fathers chase and catch their fry when they first emerge from the nest.
Parental Investment: male parental care ; pre-hatching/birth (Provisioning: Male, Protecting: Male); pre-weaning/fledging (Provisioning: Male, Protecting: Male); pre-independence (Provisioning: Male, Protecting: Male)