Genus Pimephales
Rafinesque, 1820

This genus is endemic to North America where there are 4 species in Arctic, Atlantic and Gulf of Mexico drainages. It occurs in Iran as an exotic.

These fishes are small, less than 12 cm standard length, with a stout to slender body. They are uniquely characterised by the last, unbranched dorsal fin ray in males being short, blunt and separated from the succeeding rays by a membrane. There are usually 7 branched dorsal and 6 branched anal rays. The lateral line is complete to incomplete. The head and back before the dorsal fin is flattened and the predorsal scales are small, irregularly arranged and crowded. The intestine varies from long to short, the peritoneum from black to silvery. Pharyngeal teeth are in one row. The flank has a dark band often terminating in a spot at the caudal fin base.

The species of this genus are of some commercial importance as bait or food for sport fishes.

Pimephales promelas
Rafinesque, 1820

Common names

None.

[fathead minnow].

Systematics

This exotic is unrelated to native Iranian fishes and was described from Lexington, Kentucky, U.S.A..

Key characters

This species is unique in Iran in that the last, unbranched dorsal fin ray is short and separated by a membrane from the next, longer ray in males. Other characters include the absence of a barbel, scales in front of the dorsal fin are much smaller and more crowded than flank scales, the back is flattened, the lateral line is incomplete to nearly complete, the mouth is small and terminal, and by the colour and tubercle patterns described below.

Morphology

Dorsal fin branched rays 7, rarely 8, anal branched rays 6, sometimes 7, pectoral rays 14-18 and pelvic rays 8-9. Scales in lateral series 39-56, lateral line pores usually ending before the dorsal fin origin but rarely may be almost complete. Scales are oval with a markedly anterior focus, few circuli and moderate numbers of radii restricted to the posterior field. Vertebrae number 35-38.

Pharyngeal teeth 4-4, slightly hooked at the tip, compressed and with elongate and concave cutting surfaces. The gut is elongate with several loops. Gill rakers 12-16, short and touching the adjacent raker when appressed.

Sexual dimorphism

Large tubercles in males are found on the snout in 3 (rarely 4) rows with 4-15 in the lower row, and with up to 11 tubercles on the lower jaws. There are also smaller tubercles on top of the head and pectoral rays. Tubercles first develop in early April in Canada and males begin to lose them in late July. By early September only scars remain. Males also develop a blue-black to grey, spongy, wrinkled pad on the back between the head and dorsal fin. Fin membranes swell. Breeding males darken, particularly the head and dorsal fin, and the stripe is not apparent. The body can be completely black with a white band at the head-body region and under the dorsal fin. This occurs only during aggression or sexual activity. The lateral banding enhances the robust appearance of fish which must maintain a territory over several weeks without much opportunity to feed. Weight loss is replaced by water to help maintain the image of a fat and vigorous male. Very frightened fishes blanch.

Females have a protruding ovipositor.

Colour

The back and upper flank are dark olive-green to brown, silvery to golden flanks and a whitish belly. There is a mid-flank stripe and a predorsal stripe. Scales on the upper flank are outlined by pigment. A spot at the tail base is faint to absent. Peritoneum black.

Size

Reaches 10.2 cm total length but usually much less.

Distribution

This species was reported from a reservoir, probably the Yengi Kand where bass (Micropterus salmoides) and bluegills (Lepomis macrochirus) were introduced, south of Tehran at 75 km from Asia-beg (Andersskog, 1970) (presumably Asia Bak at 35°19'N, 50°30'E on the Tehran-Esfahan highway). The MMTT catalogue also has a record for the "Dusadj Reservoir", 90 km west of Saveh, presumably in Markazi Province and the Namak Lake basin too. These reservoirs may be the same locality as "Dusadj" or Duzaj, Yang-e Kand and Yanguikand are all villages in the same general area west of Saveh. The reservoir is deduced from maps to be at about 35°19'N, 49°55'E.

A report for the Golpayegan Reservoir (Golpayegan is at 33°27'N, 50°18'E) in the Namak basin by Saadati (1977) was an error (R. J. Behnke, in litt., 1979).

? Map

Zoogeography

The fathead minnow is native to North America and was introduced to Iran accidentally in shipments of largemouth bass, Micropterus salmoides, and bluegills, Lepomis macrochirus. Fathead minnows are pond-raised in North America as food for bass.

Habitat

Fathead minnows are found in ponds, small lakes and slow-flowing brooks, often associated with vegetation. They tolerate high turbidity, high temperatures, low oxygen and high alkalinity and so are able to survive in desiccating or other conditions unfavourable to most fishes.

Age and growth

Males grow faster and larger than females, typical of nest defending species. Life span is about 3 years with maturity attained as early as 1 year, rarely in the year of birth.

Food

Food is bottom sediment for its organic content including plant material, aquatic insects and zooplankton.

Reproduction

Spawning runs from April to August in North America, once water temperatures reach 14°C and light-dark hours are 16-8. Males choose a spawning site under a log, rock, plant stems or even a lily pad or any solid artificial structure in shallow water. Cavity spawning in mud-bottomed habitats prevents the eggs from being smothered as well as offering protection from predators for the relatively few eggs spawned from a small fish. The male will clean out the cavity, spending up to 10 hours on the task, using his tubercles to scrape, pulling debris with his mouth and sweeping with his tail fin. The spongy pad on the back may serve to test spawning sites and eggs chemically. The pad secretes a mucus which is smeared on the spawning site perhaps to improve it for egg survival since mucus protects against disease and parasites. Diseased eggs are eaten by the male. The mucus may also serve to indicate ownership of a nest site. Spawning male fatheads lose their ability to produce alarm or fright chemicals on skin injury, otherwise the continual pad rubbing would disturb spawning activities by releasing alarm substance and scaring away females.

Females may enter the spawning site casually, be chased there by a male or enticed by a face to face encounter and leading to the nest. The male lifts and presses the female on her side between himself and the roof of the spawning site and the female rapidly undulates through an s-shape. Egg deposition is thought to use the same unusual mechanism as in the bluntnose minnow (Pimephales notatus (Rafinesque, 1820)). As each egg is extruded, it is transferred to the upper side of the female and the undulation rolls it along between her side and the nest cavity roof. When the adhesive egg reaches the tail she presses it against the roof where it sticks. How the female transfers the egg from her papilla to her side is unknown and the question remains why this sideways process is used when other roof spawners simply turn upside down and deposit eggs directly. The process may serve to roll eggs into a vacant roof space, occupying the roof most efficiently. Eggs laid on top of others may not attach well or prevent proper development of the underlying eggs.

Males court females by swimming rapidly up to them and then freezing at 3-5 cm away, and by leading females with a zig-zag or straight-line motion from the female to the nest site. Males will also display to females by erecting their fins for 2-3 seconds and by jump-swims in which a male swims upwards to a female then rolls on his side and swims back down. Butting and lateral quivering also occur, perhaps attempts to assess spawning condition of the female. Males defend the eggs against other fishes, including female fatheads, by using the snout tubercles to butt and tail swipes to intimidate by sending a pressure wave sensed by the lateral line system. Chasing and biting are common and 2 males may carousel (or circle head-to-tail) trying to contact each other. Leeches and turtles are also driven away. Some eggs are lost while the male is distracted chasing away predators. Repeat spawning may be necessary to replace lost eggs. Males also aerate and clean the eggs with fin movements. A nest will contain eggs in various stages of development as the male will spawn with several females. Females will deposit eggs in several nests. Orange, mature eggs are up to 1.6 mm in diameter with 12,000 or more per nest. A female will release up to 10,164 eggs in a season but from 9 to 1136 at a time. Spawning intervals are 2 to 16 days.

Parasites and predators

It is an important food for many other fishes and aquatic birds.

Economic importance

In the U.S.A. fatheads are raised as bait fish and as forage fish for introduction into bass fishing lakes. They are also used extensively as a laboratory animal for tests of toxic compounds. They have even been used to evaluate the biological effects of materials from the moon.

Conservation

This exotic species may have deleterious effects on the native fishes and its conservation is of no utility. It is extremely fecund and could compete with native species for food and habitat. A variety of parasites have been reported from this species including some which can have devastating effects on fish populations such as Ligula intestinalis. The introduction of this fish into Europe led to an outbreak of enteric redmouth disease (Yersinia ruckeri) which spread to native and farmed stocks of commercially important fishes such as trout (Michel et al., 1986; Welcomme, 1988). Native fishes may be less well adapted to withstand the depredations of exotic diseases and parasites. Ideally it should be extirpated but, if this is not possible, its interactions with native fishes should be studied and attempts made to prevent its spread to other water bodies.

Further work

The status and numbers of this exotic should be checked by field work. Any data on this exotic species held in files of the Department of the Environment should be published so that this "grey" literature is not lost to future students of Iranian fishes.

Sources

Based on North American literature summaries such as Scott and Crossman (1973) and Becker (1983) as well as personal observations. The biology of Iranian populations is unknown.