Fathead Minnow, Pimephales promelas

Fathead Minnow, Pimephales promelas, Juvenile, Female. Fish caught from within Barry Park, Syracuse, New York, June 2022. Length: 4.8 cm (1.9 inches).  Catch, photography and identification courtesy of Aidan Perkins, Long Island, New York.

Fathead Minnow, Pimephales promelas, Female. Fish caught from within Barry, Syracuse, New York, June 2022.  Length: 7.4 cm (2.9 inches). Catch, photography and identification courtesy of Aidian Perkins, Long Island, New York.

Fathead Minnow, Pimephales promelas, Female. Fish caught from the Upper Klamath Lake, Klamath Falls, Oregon, May 2015. Length: 7.5 cm (3.0 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.

Fathead Minnow, Pimephales promelas. Fish caught in the Fenton Lake, New Mexico, June 2016. Length: 7.8 cm (3.1 inches). Catch, photograph, and identification courtesy of Ben Cantrell, Peoria, Illinois.

Fathead Minnow, Pimephales promelas, Male. Fish caught from the Upper Klamath Lake, Klamath Falls, Oregon, July 2018. Length: 7.6 cm (3.0 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.

Fathead Minnow, Pimephales promelas, Breeding Male. Fish caught out of the Woods Canyon Lake, Payson, Arizona, June 2018. Length: 7.8 cm (3.1 inches).Catch, photograph and identification courtesy of Eli (obsessiveangling.wordpress.com).

Fathead Minnow, Pimephales promelas, Male. Fish caught from within Barry Park, Syracuse, New York, June 2022. Length: 8.1 cm (3.2 inches).  Catch, photography and identification courtesy of Aidian Perkins, Long Island, New York.

Fathead Minnow, Pimephales promelas, Breeding Male. Fish caught out of the Woods Canyon Lake, Payson, Arizona, June 2018. Length: 7.8 cm (3.1 inches). Catch, photograph, and identification courtesy of Chris Moore, Peoria, Arizona.

Fathead Minnow, Pimephales promelas, Male. Fish caught from Onondaga Lake Park, Syracuse, New York, June 2022. Length: 8.1 cm (3.2 inches).  Catch, photography and identification courtesy of James Lafontaine, Long Island, New York.

Fathead Minnow, Pimephales promelas, Breeding Male. Fish caught out of the Woods Canyon Lake, Payson, Arizona, June 2018. Length: 8.2 cm (3.2 inches). Catch, photograph, and identification courtesy of Chris Moore, Peoria, Arizona.

The Fathead Minnow, Pimephales promelas, is a member of the Carp and Minnow or Cyprinidae Family, and is known in Mexico as carpita cabezona. They received their common name from the flattened heads of breeding males. Globally, there are four species in the Pimephales genus, of which two are found in Mexico’s freshwater systems. Fathead Minnows are of scientific interest as they possess a distress substance called a Schreckstoff. found in epidermal club cells. Upon mechanical damage to these club cells an alarm substance is released that can be detected by other similar fishes. The other fish then engage in antipredator behaviors such as hiding or departing the area. Also, when the alarm substance is ingested by the predator, they become chemically labeled as dangerous and become easy to identify.

The Fathead Minnow has a short stout body that is laterally compressed. The adults are a dull dark olive to brown dorsally with a dusky stripe along the sides transitioning to white ventrally. They have a black peritoneum that is visible. Their head is short, blunt and broad on top with an oblique mouth. They are sexually dimorphic with males being larger than females. Their head is short and rounded with small eyes, and a small terminal mouth equipped with pharyngeal teeth. Their anal fin has 7 rays; the caudal fin is forked with rounded ends; their dorsal fin has 8 rays and is directly above the pelvic fins; their pectoral fins have 14 to 16 rays; and, their pelvic fins have 8 rays. They have 14 to 20 gill rakers (4 to 6 upper and 10 to 14 lower). They are covered with small scales. Their lateral line is short and incomplete.

The Fathead Minnow is found in lakes, ponds, headwaters, creeks, small rivers, ditches, reservoirs, and residual pools of intermittent streams, usually in sluggish or still water with abundant floating and submerged vegetation. They are tolerant of low – 2.0°C (36.6°F) and high – 33°C (91.5°F) water temperatures, turbidity, low oxygen, and high salinity. They reach a maximum of 10.9 cm (4.3 inches) in length. They are omnivores that are filter feeders. They sift through dirt and silt and feed on crustaceans, insects, aquatic invertebrates, algae, phytoplankton and detritus. In turn they are preyed upon by larger fish including Crappies, Largemouth Bass, Northern Pike, Rock Bass, Yellow Perch and Walleye, as-well-as Herons, Kingfishers, Terns, Turtles and by Crayfish and large Leeches. They have lifespans of up to 3 years. They become reproductively competent toward the end of their lifespan and usually die within 30 days of spawning. Reproductive changes commence about 30-days prior to spawning. The males begin to develop tubercles on the head and a spongy dorsal pad, and they change to a darker overall shade with more pronounced banding and the lateral line disappears. The females develop an ovipositor, a fleshy protuberance near the vent which is used to help position eggs during spawning. Fathead minnows are fractional spawners, meaning they begin spawning when water temperatures approach 18°C (64°F) and continue until the water temperature exceeds 29°C (84°F) or drops below 18°C (64°F) in late summer. Males prepare and actively defend the nesting site over an extended period until the fry depart. Each female will enter the nest and deposit between eighty and three hundred seventy buoyant, sticky eggs on the underside of a hard surface to which they attach, such as a stone or logs. Eggs hatch in five to seven days. The young grow rapidly and remain in close proximity to the nest until the yolk sac has been completely absorbed. Each female will spawn every three or four days or sixteen to twenty-six times per season with annual fecundity levels of 6,800 to 10,600 eggs. The females will use nests that already contain eggs. The males fertilize the eggs and remove the females from the nest to avoid cannibalism. Aside from guarding the nesting site, males act as curators for the eggs. Newly reproductive males will take over a nest and evict guarding males and invite new females to the nest. Egg levels in a single nest can be as high as 12,000 and can be maintained by multiple males for up to five weeks. They rely on a strong sense of smell and generally stay near the shoreline or close to weedy cover to avoid predation.

The Flathead Minnow is similar to the Bluntnose Minnow, Pimephales notatus (very blunt short snout).

The Fathead Minnow is found in all of the freshwater systems within the State of Chihuahua. They are utilized extensively as a live bait and are known to have been introduced in numerous areas via bait bucket releases.

From a conservation perspective the Fathead Minnow is currently considered to be of Least Concern with stable, widely distributed populations. A color morph, the Rosy-red Minnow, is popular within the aquarium trade and they can be bred in captivity. They are utilized extensively as live bait by both recreational and commercial fishermen. They are utilized extensively in toxicology studies as a good indicator of current ecological conditions. They have also been utilized for mosquito control in ponds, ditches and sloughs found in urban areas. They have been widely introduced to small ponds and lakes to provide a forage fish for bluegill, catfish and largemouth bass. They can tolerate wide changes of water temperatures and poor water quality, allowing them to quickly adapt to new habitats. In Europe they are blamed for the introduction of disease among eels and trout.