Fathead minnows are polygynandrous and spawn between the months of May and September, producing anywhere from 1000 to 10000 offspring per season. During breeding season, reproductively mature males are responsible for the selection and preparation of nest sites on the underside of horizontal objects (e.g., rocks, wood, and vegetation). Nest sites typically occur in shallow water, typically on a sandy substrate. Preparing nest sites requires males to utilize their mouth and tubercles to form a depression in the substrate. Once the nest is complete, males become highly territorial. Agonistic behavior is directed toward other male conspecifics, heterospecific intruders, and initially, mature females. In addition, males perform a variety of courting behaviors to attract females to their site. If a mature female is persistent, and not interested in consuming eggs that may already be present in the male's nest, the male grants her access to the nest site.
Spawning behavior in fathead minnows involves close lateral contact, body vibrations, and swimming back and forth in the nest area. Once adequate stimulation is obtained, males make contact with the urogenital region of the female, causing the release of eggs along with the simultaneous release of milt prior to their sudden separation. This occurs sporadically until the male aggressively drives away the female. All of the buoyant, adhesive, fertilized eggs are then deposited in a single layer on the ceiling of the nest site and thus, the male is left to care for the eggs on his own.
Mating System: polygynandrous (promiscuous)
Being oviparous and a fractional spawner (i.e., females spawn multiple times per breeding season), female fathead minnows may deposit 400 eggs per spawn, normally taking approximately 2 hours to perform each spawning sequence. Females may spawn between 16 and 26 times between May and September. Eggs are normally deposited at night, and each fertilized egg takes 4 to 5 days to hatch at 25°C, though it can take up to 13 days at cooler temperatures (15°C). Both sexes reach reproductive maturity between 4 and 5 months after fertilization. Fathead minnows grow rapidly, and despite high postspawning mortality, multiple generations may be alive at the same time.
Breeding interval: Female fathead minnows may participate in 16 to 26 spawnings per season.
Breeding season: Spawning occurs from May to September at water temperatures ranging from 16°C to 30°C.
Range number of offspring: 1000 to 10000.
Range time to hatching: 4 to 13 days.
Range time to independence: 4 to 5 days.
Range age at sexual or reproductive maturity (female): 4 to 5 months.
Range age at sexual or reproductive maturity (male): 4 to 5 months.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
Male fathead minnows invest a great deal of time and energy into caring for fertilized eggs. To sustain energetic demands, males rely on somatic energy reserves. If these reserves are insufficient, male fathead minnows tend to consume a number of their eggs in order to meet energetic demands. In addition to creating the nest site, males fan nest eggs to maintain sufficient oxygenation, utilize their dorsal pad to clean eggs, and defend against predators until hatching occurs. Fathead minnows spawn numerous times a season, thus, male energy expenditure during this time is significant. In addition, females prefer to deposit eggs in the nest of males that already possess eggs, while alloparental care augments the likelihood of new fertilization.
Parental Investment: male parental care ; pre-hatching/birth (Protecting: Male)