Topminnows belong to the Family Fundulidae, Order Cypriniformes, and Class Actinopterygii. This family also includes some North American killifishes. There are approximately forty-four to forty-six species that are found in the lowlands of North and Central America from southeastern Canada to the Yucatan Peninsula of Mexico, including the Mississippi River drainage, and the islands of Bermuda and Cuba. Most (forty species) of topminnows belong to the genus Fundulus, and others are included in the genera Lucania (three species) and Leptolucania (a single species). The Family Fundulidae is a paraphyletic grouping of members of genera Fundulus and Lucania. There are six species of topminnows found in Arkansas.
Topminnows occur in both freshwater and marine waters as well as brackish environments. They are very tolerant of a variety of temperatures and salinities. Most are small fishes under 10 cm (4.0 in.) in length, but the giant killifish (Fundulus grandissimus) of Central America and the northern studfish (Fundulus catenatus) of North America (including Arkansas) can be up to 20 cm (8.0 in.) long. As the common name implies, topminnows spend most of their time near the surface in backwater areas. Many are popular aquarium fish, and several species are invaluable model systems for comparative, environmental, and evolutionary research studies. They also likely serve as prey for many game fishes.
Topminnows possess an upturned (superior) mouth and dorsoventrally flattened head and dorsum that allows them to exploit insect and other invertebrate prey by skimming at the water surface. However, the distinguishing characteristic of the family is a twisted maxillary bone, which is straight in other fishes. In Arkansas, all six species of topminnows possess seven to sixteen soft dorsal rays, ten to eighteen soft anal fin rays with a branched third ray, and a deep groove separating the upper jaw from the snout. The origin of the pelvic fins is closer to the tip of snout rather than to the base of the caudal fin, they have a rounded caudal fin, their bodies are covered by cycloid (smooth-edged) scales, and the lateral line is absent.
There is extensive sexual dimorphism among topminnows, especially during the breeding season. Males possess longer and more-pointed fins, and their color pattern is vivid, whereas females are drab. Males also develop “contact organs” during spawns, and females have a fleshy sheath around the front of the anal fin.
Blair’s starhead topminnow (Fundulus blairae) was not reported in Arkansas until 1977. It is Arkansas’s smallest topminnow, with a maximum size of about 80 mm (3.1 in.). This topminnow possesses a prominent, dark, wedge-shaped bar extending downward below the eye (subocular teardrop). There are generally seven (from six to eight) dorsal rays, thirteen (eleven to fourteen) pectoral rays, and ten (eight to eleven) anal rays. Its body coloration is greenish-yellow above with a large golden spot on the top of the head; sides are yellowish-tan with brown stripes in the female and scattered red dots in the male.
The entire range of F. blairae includes the Gulf Slope drainages from the Escambia River of Alabama and Florida, west to the Brazos River in Texas, and north into the Red River drainage of southwestern Arkansas and southeastern Oklahoma. In Arkansas, F. blairae is considered rare and has a very restricted distribution in the southwestern part of the state in the western Saline and Little rivers of the Red River drainage. This topminnow prefers heavily vegetated borrow ditches, oxbow lakes, sloughs, small creeks, streams, and swampy backwaters where the water is often tannin-stained. It is usually found swimming near aquatic vegetation, including duckweed, watermilfoil (Myriophyllum), and pondweed (Potamogeton).
Little is known about the reproductive biology of this fundulid in Arkansas. Females with eggs have been collected from mid-May to July from a private pond near the Rolling Fork backwater in Sevier County. At the same time, males were reported to be in full breeding color. This fish is listed as a Species of Greatest Conservation Need in Arkansas.
The northern studfish (Fundulus catenatus) is distributed disjunctly east of the Mississippi River in Indiana, Illinois, Kentucky, Tennessee, Virginia, Alabama, Louisiana (Florida parishes), and southwestern Mississippi, and west of the Mississippi River to the Interior Highlands of Arkansas, central and southern Missouri, southeastern Kansas, and eastern Oklahoma. In Arkansas, the northern studfish occurs in the Ouachita Mountains of the Red and Ouachita river drainages, in the Ozark Mountains of the Illinois and White river drainages, and in a few tributaries of the Arkansas River. Unlike most other Arkansas topminnows, F. catenatus inhabits clear mountain streams and rivers of moderate to high gradient with permanent flow where it can be found along margins of pools in quiet, shallow waters having gravel and rock substrate.
This topminnow is Arkansas’s largest, sometimes reaching 178 mm (7.0 in.) in length. It has a yellowish-brown dorsum with silver sides containing eight to ten thin horizontal interrupted lines. Breeding (nuptial) males are brightly colored with brilliant blue sides with reddish brown or orange streaks. Dorsal rays number thirteen to sixteen, and anal rays number fourteen to eighteen.
Fundulus catenatus is mostly a surface feeder, eating insects and small mollusks, but has also been reported to feed on the bottom. In Arkansas, some odd prey, including a cicada and ants, have been reported from stomach contents of this topminnow from Ten Mile Creek in Saline County and the Caddo River in Montgomery County, respectively.
This topminnow has a protracted spawning period, breeding from mid-May to early August. Males do not form nests but do establish small territories in quiet, shallow waters over gravel substrate where females deposit eggs. Two females with eggs were reported in May from Walnut Creek and Bear Creek, both in Garland County.
The golden topminnow (Fundulus chrysotus) is strictly a lowland species found in shallow sloughs, swamps, and vegetated pools and backwaters of sluggish creeks but can also be found in small to medium rivers; it occasionally occurs in brackish water along the Gulf Coast. This topminnow ranges from the coastal plain of South Carolina west to the Trinity River of Texas north through the Mississippi River Embayment to southwestern Kentucky and northeastern Tennessee. In Arkansas, F. chrysotus can be found in widely scattered locales of all major drainages of the Gulf Coastal Plain lowlands in the southern and eastern part of the state.
Male F. chrysotus are yellowish-green with reddish-brown spots, small golden flecks, and dusky vertical bars on its side. Females and juveniles are uniform olive-green with small blue spots on the sides, without the intensity of the male coloration. There are seven to nine dorsal rays and nine to eleven anal rays. This is a small topminnow with a maximum size of 80 mm (3.2 in.).
Very little is known regarding the reproductive biology of this topminnow. Three females with mature eggs were reported in April from Calion Spillway at Calion Lake in Union County. Also, a female with eggs was reported being pursued by several adult males in full breeding coloration in July at Cane Creek Lake in Lincoln County. Similar to other topminnows, F. chrysotus takes insects at the water surface.
The northern starhead topminnow (Fundulus dispar) is found in the southern tributaries to Lake Michigan south through the lowlands of the Mississippi River from Illinois to the Ouachita River drainage of Arkansas east to the Mobile Basin. In Arkansas, this topminnow is primarily a Coastal Plain inhabitant found in river drainages of the lower Arkansas, Ouachita, eastern Saline, St. Francis, and lower White in the southern and eastern part of the state. It occurs in backwaters, ditches, oxbows, sluggish waters of creeks, and swampy backwater overflows of rivers. It prefers clear water and, like the morphologically similar F. blairae, is found associated with aquatic vegetation, where it feeds on snails, crustaceans, aquatic and terrestrial insects, and algae.
Little is known about the reproductive biology of this topminnow. It is known to spawn in late spring to early summer. A female containing eggs was reported in April below the Calion Spillway at Calion Lake in Union County. The largest specimen of F. dispar was reported to be 81 mm (3.2 in.).
The blackstripe topminnow (Fundulus notatus) is a medium-sized fundulid that ranges from the Great Lakes tributaries and Mississippi River basins from southern Ontario south to the Gulf Coast. It is found primarily in lowland, slow-flowing semi-turbid streams and slack-water areas below the Fall Line of southern and eastern Arkansas.
Fundulus notatus is olive-brown to pale brownish yellow on its dorsum and upper sides with a few (if present) small, scattered, diffuse spots that are indistinct. The underside is white, and the lateral band is usually straight-edged in females, whereas in males, the vertical streaks are serrate and extend from the lateral band. There are usually nine to ten (from eight to twelve) dorsal rays and usually twelve to thirteen (eleven to fourteen) anal rays. The maximum length of F. notatus is about 76 mm (3.0 in.).
Breeding occurs in late spring to early summer in submerged vegetation, where males defend loose territories and court females. Prey is similar to that of other topminnows and includes terrestrial arthropods, aquatic insects, and filamentous algae.
The blackspotted topminnow (Fundulus olivaceus) is very similar to F. notatus but differs in having small but prominent black spots in outline on its dorsolateral sides. The dorsal fin rays number nine to ten (eight to twelve) and the anal rays number eleven to thirteen (ten to fourteen). It is about the same color overall as F. notatus. The maximum length of F. olivaceus is 97 mm (3.8 in.) and its lifespan, like that of most topminnows, is about three years.
This topminnow is widespread and abundant in the central and lower Mississippi River Basin and Gulf Coastal drainages from Florida through the San Jacinto River, Texas. In Arkansas, it is one of the widest-ranging topminnows and is distributed statewide in all river drainages.
Ecologically, it is also similar to F. notatus in reproductive behavior as well as its food habits. This topminnow occurs in small to medium streams with moderate current, and small schools of F. olivaceus usually swim near the stream margin. However, it seems to differ from F. notatus in preference for slightly faster-flowing streams and appears to avoid the sluggish downstream regions occupied by the blackstripe topminnow.
There are numerous parasites reported from fundulids in North America. In Arkansas, several helminth parasites have been reported for the first time from F. catenatus, F. notatus, and F. olivaceus. A new species of trematode was recently described from F. notatus from southeastern Oklahoma.
For additional information:
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Chris T. McAllister
Eastern Oklahoma State College
Last Updated: 12/11/2018