When the photoperiod and temperature requirements are met, adult brook stickleback move from deeper water into the warmer, shallow waters along the shoreline where vegetation is plentiful. The males establish territories and begin nest construction; they also change coloration from the non-mating olive to dark green or black. They typically construct the nest on a vertical piece of grass or a stick by using materials such as algae, plant fibers, dead leaves and small twigs (Reisman and Cade 1967, Winn 1960). The organic materials are held together by a white secretion from the kidneys and other related organs. The nests are initially built with one opening (Barker 1918).
As the male builds the nest he aggressively defends his territory from male and female conspecifics as well as other species like trout, Gambusia and darters (Winn 1960). The male may perform a “lateral display” at his territorial borders to warn potential intruders by slightly undulating his body while extending the ventral and dorsal spines. This display typically leads to fighting and the male will chase intruders from his territory until he crosses into the territory of another and is in turn chased (Reisman and Cade 1967). The territorial aggressions of the male toward an encroaching fish are very high during nest building. Once the nest is built aggressiveness remains high, but is more intense toward males than toward potential mates. Aggressive behavior diminishes toward all intruders when egg nurturing is required. Aggressiveness toward all intruders then becomes more prominent once the larvae have hatched and are free swimming (Ward and McLennon 2006).
Once the nest is complete, the male performs a “tail flagging” dance to attract gravid females. Dancing was observed on occasion in a laboratory setting and was not necessary for reproduction (Reisman and Cade 1967). To begin the dance, the male swims towards a female and stops in front of her with his head down and his whitish tail held high above his back. He then waves the tail back and forth counteracting any forward momentum with the pectoral fins. Once the dance is performed the male moves toward the nest with the same movement.
A female entering the territory of a male is attacked and will take one of four actions: move toward the nest, remain motionless, drop to the bottom or leave for another territory (Winn 1960). If the female moves toward the nest ahead of the male she will be attacked and chased out of his territory. If the female remains motionless or drops to the bottom, the male may move toward the opening of the nest. The female will then enter the nest headfirst with her tail sticking out the entry hole. Males are more likely to choose nuptially colored females with a variegated dark and light pattern as mates over gravid plain colored females (McLennon 1995). The male then prods the ventral portion of the female’s caudal peduncle and the female responds by laying her eggs. This male prodding action usually occurs numerous times during the egg laying process. When the female finishes laying her eggs she swims out the back of the nest creating a second hole and is attacked by the male. Once the female leaves the area, the male quickly swims through the nest to fertilize the eggs (Becker 1983, Winn 1960). The male may or may not repair the hole created by the female. More than one female may lay her eggs within the nest and on occasion males may actually build and maintain more than one nest (Winn 1960).
Mating System: polygynous
Culaea inconstans are iteroparous and spawn in the spring and early summer typically from mid-April to late June depending on range location. Spawning initiation is influenced by photoperiod requirements of between 14 and 16 hours of sunlight (Reisman and Cade 1967) and also by temperature requirements between 15 and 19°C (Barker 1918, Reisman and Cade 1967, Winn 1960). Females lay between 92 and 182 eggs per clutch which hatch after 7 to 11 days. Both male and female brook stickleback are able to reproduce at 1 year of age.
Breeding interval: Brook stickleback breed once a year.
Breeding season: Brook stickleback breed from mid-April to late June depending on range location.
Range number of offspring: 92 to 182.
Range time to hatching: 7 to 11 days.
Average time to hatching: 10 days.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; sexual ; fertilization (External ); oviparous
Once eggs are fertilized the male pushes them to the sides of the nest and down into the nest material. He then takes a position in front of the nest entrance and begins to aerate the eggs by fanning his pectoral fins (Barker 1918, McKenzie 1974, Tomelleri and Eberle 1990, Winn 1960). After 9 to 11 days the eggs will hatch and the male responds by pulling apart the top of the nest to create more space between the organic debris, thereby creating a nursery for the larvae (McKenzie 1974). The larvae float up to the top of the nursery sometimes escaping and making their way to the surface of the water. The adult male gathers the escapees in his mouth and spits them back into the nursery. He continues to retrieve larvae for a day or two until the rate at which they escape is faster than the rate that he can retrieve them. At this time he either abandons the larvae or eats them (Becker 1983, McKenzie 1974).
Parental Investment: male parental care ; pre-fertilization (Provisioning, Protecting: Male, Female); pre-hatching/birth (Provisioning: Male, Protecting: Male); pre-weaning/fledging (Protecting: Male); pre-independence (Protecting: Male)