Fathead minnows utilize chemical cues to differentiate between familiar (i.e., shoalmates) and unfamiliar individuals. Olfactory signals vary in relation to diet, social status, parasite load, and predation risk. Chemical signaling can occur involuntarily due to the release of an alarm signal as a result of mechanical cellular damage, or voluntarily as in the release of sexual pheromones during courtship. During breeding season, males also perform both stationary and dynamic courtship displays in order to attract females to nest sites.
Communication Channels: visual ; tactile ; chemical
Other Communication Modes: pheromones
Perception Channels: visual ; tactile ; chemical
Fathead minnows are commonly preyed upon by piscivorous fish such as northern pike, yellow perch, largemouth bass and walleye. An important antipredator tactic is their ability to warn conspecifics of potential threats via pheromones. From distinctive epidermal club cells, fathead minnows release an alarm substance in response to mechanical cell damage other species of the nearby threat. Such cues also have the potential to attract additional predators that could disrupt the predation event. If others can disrupt the predation event and facilitate escape, warning signals may benefit other species as well as wounded prey. Interestingly, mature males lose this capability during the breeding months.
Known Predators:
Fathead minnows are characterized by deep, compressed bodies, typically five to eight centimeters in length, and a short head that is dorsally flattened with a blunt snout, round lateral eyes, and terminal, upturned mouth. With the exception of a dark blotch at the rostral end of the dorsal fin, their fins are generally clear. Fathead minnows are dark-olive colored with a dusky, dorsal and lateral stripe, and yellow to white underbelly. They have an incomplete lateral line, 8 dorsal rays, 7 anal rays, 14 to 17 pectoral rays, 7 to 8 pelvic rays, pharyngeal teeth, and smaller scales along the nape. Males and females vary in size, banding, and secondary sexual characteristics, however, males and females are virtually indistinguishable until reproductive maturity. Adult males range from 3 to 5 g, while adult females are slightly smaller, ranging from 2 to 3 g. Additionally, males have dark heads with 2 white to gold vertical bars posterior to the head and dorsal fin. Males also have a fleshy, dorsal pad and 16 nuptial tubercles on the lower jaw. Although females do not undergo such obvious changes in morphology, they do develop a fleshy ovipositor approximately a month prior to spawning.
Range mass: 2 to 5 g.
Range length: 5 to 8 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: male larger; sexes colored or patterned differently; male more colorful; ornamentation
On average, fathead minnows live two to three years in the wild and may be limited by high levels of postspawning mortality. Fathead minnows can live for up to 4 years in captivity.
Range lifespan
Status: captivity: 4 (high) years.
Typical lifespan
Status: wild: 2 to 3 years.
In addition to small rivers and ponds,fFathead minnows are commonly found in muddy pools of headwaters and creeks. They also appear to tolerate habitat conditions that exclude many freshwater fishes such as high turbidity and temperature, variable pH and salinity, and low oxygen. Residing in such habitats may be important in decreasing risk of predation, as many predatory fish are intolerant of such conditions.
Habitat Regions: temperate ; freshwater
Aquatic Biomes: lakes and ponds; rivers and streams; temporary pools
Wetlands: marsh
Fathead minnows are native to the Nearctic region. The northern limits of their geographic ranges extends from Quebec to Alberta and Northwest Territories, Canada. Their southern limites of their geographic range extends as far southward as Alabama, Texas, and New Mexico. Fathead minnows are most abundant in the Prairie Pothole Region of the northern Great Plains. Bait-bucket introductions have also occurred in the Mobile Bay drainage, Colorado River drainage, Alabama, Arizona, New Mexico, and Mexico. They are generally absent in mountainous regions as well as on the Atlantic Slope of Delaware River. They have also been introduced in Europe (Belgium, France, Germany, and the United Kingdom), Puerto Rico, and Iran.
Biogeographic Regions: nearctic (Introduced , Native ); palearctic (Introduced )
Fathead minnows are opportunistic omnivores that can be characterized as benthic filter feeders, sifting through mud and silt in order to find food. Freshwater sediments often contain a large abundance of algae and protozoans, which represent a significant proportion of the fathead minnow diet. Secondary prey items include diatoms, filamentous algae, small crustaceans, and insect larvae. In addition, brook sticklebacks represent one of few species also common within the Prairie Pothole Region that also prey heavily on zooplankton, placing a high probability of interspecific competition between brook sticklebacks and fathead minnows. Differences in size-selection and feeding strategies, however, allow fathead minnows to consume a broader variety of zooplankton prey. Flexibility in feeding may explain why greater densities of fathead minnows exist in this region as compared to brook sticklebacks.
Animal Foods: insects; aquatic crustaceans; other marine invertebrates; zooplankton
Plant Foods: algae; phytoplankton
Other Foods: detritus
Foraging Behavior: filter-feeding
Primary Diet: carnivore (Eats non-insect arthropods); herbivore (Algivore); omnivore
Secluded basins and harmful conditions in the Prairie Pothole Region result in a simple fish community, with fathead minnows and brook sticklebacks being the most common species in this region. Fathead minnows are often the dominant species and experience explosive population growth with the absence of piscivorus fish and their high reproductive rate. This allows fathead minnows to reach biomass estimates ranging from 144 to 482 kg/ha during the breeding season. With both high population numbers and biomass, it is not a surprise that fathead minnows possess significant influence on the aquatic macroinvertebrate populations, one of their primary food sources. Populations of zooplankton, aquatic insects, and ostracods are greatly affected by fathead minnow predation, with peak daily consumption ranging from 10.1 to 62.6 kg/ha. Thus, fathead minnows indirectly affect species dependent on aquatic invertebrates as food, such as ducks and their young, larval salamanders, and a number of passerine birds. Higher turbidity and phytoplankton biomass also result in wetlands with the presence of fathead minnows. However, the structure of these systems is strongly dependent on the presence and abundance of fathead minnows as a low- to middle-level consumer, whether it be due to direct or indirect effects. In addition, because they are tolerant of a broad range of environmental conditions, fathead minnows are common among in a large variety of aquatic habitats throughout its geographic range. Fathead minnows represent an important food source for piscivorous fishes, as they often the only species present in human-made retention ponds due to their habitat adaptability.
Ecosystem Impact: keystone species
Fathead minnows are significant contributors to global toxicology and behavioral ecology research due to their relatively short lifespan and high reproductive rate. Likewise, it has become the most widely utilized North American model for ecotoxicology since the mid-twentieth century. They also play a significant role in fisheries as prey for important commercial and recreational fish species. Albino fathead minnows, often referred to as "rosy-red minnows," are commonly used as bait for recreational fishing, and are also used as a feeder fish in bass-bream ponds. Albino fathead minnows are commonly found in aquaria, with both sexes possessing red-orange body and fins.
Positive Impacts: pet trade ; research and education
Although widely distributed across North America, introductions of fathead minnows as a bait species in Europe have resulted in devastating effects on the wildlife in northern Europe. Its introduction in Europe resulted in the co-introduction of enteric redmouth disease, an organism that negatively affects wild and cultured trout and eels.
After fertilization, fathead minnow eggs are approximately 1.4 mm to 1.6 mm in diameter. Following several well-defined embryonic stages, eggs hatch within 4 to 5 days at 25°C. Upon hatching, fathead minnow larvae absorb the yolk sac within 1 to 2 days, afterwhich larvae become active feeders preying upon live food. These protolarvae range in length from 4.0 mm to 5.2 mm and can be characterized by an incomplete mouth, dark eyes, rudimentary pectoral fins, melanophores, which are widely distributed on the yolk sac and concentrated in regions posterior to the vent. Contrastingly, mesolarvae and metalarvae possess high concentrations of melanophores on the ventral surface of gill covers. The number of myomeres between protolarvae and mesolarvae, and metalarvae differ only slightly, with the metalarvae possessing a slightly more in the predorsal region and a few less in the postanal region. All larval stages have rounded rather than flattened eyes, similar to 'bluntnose minnows Pimephales notatus'.
Reproductive maturity in fathead minnows is identified by a number of morphological changes in both males in females. For example, males develop a dorsal pad, tubercles on their lower jaw, and banding changes. Just prior to maturation, females develop urogenital papillae. Fathead minnows reach sexual maturity within 4 to 5 months after hatching in optimal habitat conditions (e.g., water temperature of 25°C and photoperiod of 16 hours of light). Once mature and under appropriate seasonal conditions, minnows can spawn continually for a period of several months.
Fathead minnows are among the most prevalent fish species in eastern North America. The species is considered secure and has stable populations. The widespread nature of this species may be attributed to its ability to adapt to a variety of aquatic habitats and conditions as well as its high reproductive rate.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
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 gestation period: 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)
Fathead minnow (Pimephales promelas), also known as fathead or tuffy, is a species of temperate freshwater fish belonging to the genus Pimephales of the cyprinid family. The natural geographic range extends throughout much of North America, from central Canada south along the Rockies to Texas, and east to Virginia and the Northeastern United States.[2] This minnow has also been introduced to many other areas via bait bucket releases. Its golden, or xanthic, strain, known as the rosy-red minnow, is a very common feeder fish sold in the United States and Canada. This fish is best known for producing Schreckstoff (a distress signal).
The fathead minnow in its wild form is generally dull olive-grey in appearance, with a dusky stripe extending along the back and side, and a lighter belly. There is a dusky blotch midway on the dorsal fin. Breeding males acquire a large, grey fleshy growth on the nape, as well as approximately 16 white breeding tubercles on the snout.[2][3]
Typical total lengths are between 7 and 10 cm.[4][5]
Fathead minnows are distributed across North America from Chihuahua, Mexico, north to the Maritime Provinces and Great Slave Lake drainage of Canada and have been introduced to Atlantic and Pacific coastal drainage basins in the United States.[6] Their tolerance for multiple environmental conditions, characteristics of their life history, and their popularity as bait species contribute to their widespread distribution.[6] The fathead minnow is quite tolerant of turbid, low-oxygen water and can most commonly be found in small lakes, ponds, and wetlands. They can also be found in larger lakes, streams, and other habitats, as well.[6]
Fathead minnows are omnivores that are categorized as Benthic filter feeders, sifting through dirt and silt to find food. The carnivorous portion of their diet is made up of mainly insects, crustaceans, other aquatic invertebrates, and zooplankton. The herbivorous portion of their diet is primarily made up of algae and phytoplankton. Fathead minnows will also feed on bottom detritus.
Fathead minnows are a largely preyed upon fish that is eaten by mainly piscivorous fish such as Largemouth Bass, Northern Pike, Yellow Perch, Walleye, and various other types of fish.[7]
Ostariophysan fishes, which include fathead minnows, possess an alarm substance, or Schreckstoff, in distinctive epidermal club cells. The alarm substance is released upon mechanical damage to these club cells due to a predator attack, and can be detected by other ostariophysan fishes which then engage in antipredator behaviors such as hiding or dashing away.[8] Fathead minnows learn to recognize an animal as a potential predator when it is presented in conjunction with the alarm substance. Also, alarm substance ingested by the predator will chemically label it as dangerous to naïve fathead minnows, thereby resulting in learned predator recognition.[8] Prey fishes with chemical predator recognition abilities can inhabit areas with low visibility and more quickly detect ambush predators like the fathead minnow's primary predator, the northern pike.[9]
In the fathead minnow, the female supplies the eggs and the male cares for them until they hatch. The male defends a nest as females pass by and spawn eggs to be cared for by the male. In choosing a nest site, the newly reproductive male fathead minnow tends to take over the nest site of a parental male and evicting its resident rather than occupying an empty one.[10] Also, when given the choice between different unguarded nest sites, it will usually choose the one that already contains eggs. The newer and more numerous the eggs are in the nest site, the more likely the current male is to be challenged by the newcomer.[10] The new male will care for the old male's eggs, a behavior called allopaternal care. Paternal care of the eggs by the male includes rubbing the dorsal pad of mucus-secreting cells, which aerates the eggs and may help prevent disease; removing of diseased eggs from the clutch; and defending the clutch from egg predators, which include animals such as crayfish.[10] This has been shown to increase the survival of the eggs, probably because the newer male is fitter and better able to protect them than the former. Egg survival and parental care behaviors also increase as the clutch size increases.[10] Females also prefer to spawn with males that already have eggs in their nest sites, and the more the better. A male fathead minnow defends the nest site for about three to five weeks at a time, thus continual turnover of new males in the population occurs. The cost of allopaternal care is relatively small because fathead minnow eggs hatch in about five days, while the males can maintain a nest for about three to five weeks; thus, only a small proportion of the eggs that the male takes care of will ever have been adopted.[11]
The main spawning season of the fathead minnow is from June through July, and they are in good spawning condition from mid-May to early August. In males, tubercles occur from mid-May to early August with peak development going from June to July, at the same time as other indicators of reproductive condition.[12] In males, epidermal thickness is significantly higher between mid July and early August, but it stays constant in females. Mucous cell counts also rise in males during the breeding season, but it stays constant in females. The chemical alarm signal in the epidermal cells also drops to almost zero in males during the breeding season.[12]
Fathead minnows are fractional spawners, meaning they begin spawning when water temperatures approach 18 °C (64 °F) and continue until they drop below that temperature in late summer. Fractional spawning can result in 16 to 26 spawning events per female and an annual fecundity of 6,800 to 10,600 eggs per female. Juveniles display rapid growth, reaching 45–50 mm total length in 90 days, and most fathead minnows die after spawning by the age of one year.[12]
Spawning can be affected by artificial estrogen, which can get from oral contraceptive pills to lakes via wastewater. Artificial estrogen feminizes male fathead minnows such that they produce vitellogenin, a protein involved in oocyte maturation, and alters oogenesis in female fathead minnows.[13] Chronic exposure to EE, an artificial estrogen used in oral contraceptive pills, led to the collapse of the population due to reduced spawning in a seven-year whole-ecosystem study at the Experimental Lakes Area in Ontario, Canada.[13]
Because the fathead minnow is fairly tolerant of harsh conditions, it can be found in bodies of water that may be uninhabitable to other fish, such as waste drainage sites. It has also been studied to investigate the effects of these waste materials on the aquatic life.
Natural and synthetic oestrogens, such as oestradiol and oestrone, are present in sewage treatment works effluents. In male fathead minnows, exposure to these steroidal compounds leads to an increase in plasma vitellogenin levels exceeding that of even mature female fathead minnows. Vitellogenin blood plasma levels are an indicator for determining if chemicals have an oestrogenic activity to fish. This is also accompanied by an inhibition of testicular growth, even if the exposure is in low concentrations or for a short period of time. These studies showed that the presence of natural oestrogens, likely originating from humans, represents a new ecotoxicological issue.[14]
Bisphenol A is a chemical used to make polycarbonate plastic, epoxy resin, and other chemicals. It is also weakly estrogenic, and many of the same effects of oestradiol and oestrone can be seen with this compound. In the male fathead minnows, reduced somatic growth is seen. With females, egg production and hatchability are reduced. The effects take place more quickly in females than in males, though.[15]
The effect of low pH on the fathead minnow has also been studied. Though survival was minimally affected by extended exposure to low pH, the minnow behavior was abnormal. They showed stress behaviors, such as surface swimming and hyperactivity.[16] In addition, some deformities also were brought about by long exposure to low pH. In both males and females, their heads became smaller than normal. Males lose some of the brightness of their color. Females become heavy with eggs but may not spawn, and the number of eggs per female is reduced. The eggs themselves come out abnormal, fragile and lacking turgidity, and the lower the pH, the less likely the eggs are to eventually hatch.[16]
In fathead minnows exposed to cattle feedlot effluent, the males are feminized and the females are defeminized. The male fathead minnows have reduced testicular testosterone synthesis, altered head morphometrics, and smaller testis size, while the females have a decreased estrogen:androgen ratio, which is defeminized sex hormone ratio.[17]
The fathead has been very commonly used as a baitfish, and more recently has emerged in the aquarium trade as the rosy-red minnow. This colour morph was discovered in several Arkansas breeding farms in 1985. Both sexes of this strain have a rosy-golden body and fins and may express dark splotches of wild-type fathead coloration, and are sold in pet shops primarily as feeder fish. They can also be used in home aquariums as pets.[18]
The fathead's invasive status in Europe is cited as the main cause for the spread of enteric redmouth disease among trout and eels there.[19] Established feral populations have been found in France (in 1991), Flanders in Belgium (1995), the Netherlands (2008) and Germany (2015).[20] A small UK population, first discovered in 2008, was declared eradicated the same year.[21]
This species is also important as an indicator species, a biological model in aquatic toxicology studies, similar to Ceriodaphnia dubia, Hyalella azteca, or Chironomus dilutus. Because of its relative hardiness and large number of offspring produced, EPA guidelines outline its use for the evaluation of acute and chronic toxicity of samples or chemical species in vertebrate animals.[22]
Generally only the rosy-red variety is sold in pet shops (though very often several wild types come in with each shipment), and is summarily the most likely to be found in an aquarium. These fish are social, active, and moderately hardy. Like most cyprinids, they will accept almost any type of food. They can be bred in an aquarium, and the fathead minnow is one of the only cyprinids that protects its eggs in the nest (carried out by the male). Fatheads will live about two years if they have spawned, but significantly longer (potentially up to four years) if they have not.[23]
The fish can be found at many pet stores as a feeder fish under the name "rosy-red minnow". In an aquarium the fish needs to be in a school (at least 5 or 6) or it tends to be territorial but will not nip fins but instead will ram its head into other species of fish and briefly chase them.
These fish prefer a temperature of 10 – 21 °C (50 – 70 °F) and a pH range of 7.0 – 7.5.[3][18]
Fathead minnow (Pimephales promelas), also known as fathead or tuffy, is a species of temperate freshwater fish belonging to the genus Pimephales of the cyprinid family. The natural geographic range extends throughout much of North America, from central Canada south along the Rockies to Texas, and east to Virginia and the Northeastern United States. This minnow has also been introduced to many other areas via bait bucket releases. Its golden, or xanthic, strain, known as the rosy-red minnow, is a very common feeder fish sold in the United States and Canada. This fish is best known for producing Schreckstoff (a distress signal).
