Fundulus dispar

starhead topminnow

Type Locality

Creeks near East St. Louis, Illinois, and Illinois River near Beardstown (Agassiz 1854).

Etymology/Derivation of Scientific Name

Fundulus, Latin diminutive of fundus, “bottom”; dispar, Latin dispar, “dissimilar, different” (Boschung and Mayden 2004).

Synonymy

Zygonectes dispar (Agassiz 1854).

Characters

Maximum size: 81 mm TL (Pflieger 1975).

Coloration: Black teardrop-shaped suborbital bar. Vertical bars on side (absent in females). Back and sides olive green, flanks are iridescent blue, belly is silvery-white. Males have 3-7 rows of large discrete spots along the sides. Females lack the discrete spots; have 7-9 horizontal lines on the sides, with spaces between lines generally unpigmented. In both males and females, the back is peppered with very small dots, and there is a narrow, dark predorsal stripe. Males and juveniles have 6-9 (3-12) reddish brown vertical bars along the sides. Fins are generally clear except for small melanophores near the fin rays. Males have rows of distinct spots on the dorsal, caudal, and anal fins, with the spots more prominent near the fin base (Ross 2001; Wiley 1977). Taylor and Burr (1997) noted male nuptial coloration included an iridescent blue hue in the head region and black spots on the anal and dorsal fins, which intensified in color and distinctness during spawning.

Counts: 34-38 (31-38) lateral line scales, 5-6 gill rakers, 6-8 dorsal rays, 9-11 anal rays, 11-12 (10-14) pectoral rays, 6 pelvic rays (Ross 2001).

Body shape: Mouth position supraterminal (Simon 1999). Slender topminnow. Head length goes into SL 3.5-4.0 times; body depth goes into head length 1.1-1.4 times (Ross 2001).

External morphology: Rounded caudal fin. Top of the head is flat.  Head usually has a scale pattern in which the large anterior scale overlaps the two scales just posterior to it (G-type). Two to three mandibular pores. Pores 4a and 4b, located on top of the head above the eye, are widely separated. Dorsal fin is posterior to the anal fin origin (Ross 2001).

Distribution (Native and Introduced)

U.S. distribution: Central Mississippi River drainage from the Ouachita River drainage, Louisiana, north to the Wisconsin River drainage, Wisconsin, and east to the headwaters of the Kankakee River drainage, Indiana (Wiley 1980; Page and Burr 1991).

Texas distribution:

Abundance/Conservation status (Federal, State, NGO)

Species currently stable in the southern United States (Warren et al. 2000). Locally common but becoming less so as wetlands are drained (Page and Burr 1991).

Habitat Associations

Macrohabitat: Commonly inhabits swamps, marshes, well-vegetated ponds and lakes, and small streams (Wiley 1980).

Mesohabitat: Inhabits clear water where aquatic vegetation is abundant; substrate is usually composed of soft mud and detritus (Boschung and Mayden 2004).

Biology

Spawning season: Late spring and early summer (Smith 1979). Mid-April to mid-July at a temperature of 17-30 C (Taylor and Burr 1997). Etnier and Starnes (1993) noted tiny tubercles on dorsal and anal fin rays in an adult male F. dispar from Reelfoot Lake, Tennessee, 20 June, but not in April or May specimens (other members of the F. notti species group, of which F. dispar is a member, develop nuptial tubercles on dorsal and anal fin rays).

Spawning habitat: Phytolithophils; nonobligatory plant spawner that deposit eggs on submerged items, have late hatching larvae with cement glands in free embryos, have larvae with moderately developed respiratory structures, and have larvae that are photophobic (Simon 1999; Balon 1981).

Spawning Behavior: Spawning position is parallel, with posterior one-third of bodies pressed together, against vegetation or substrate; most frequently attach eggs to submersed or bottom vegetation (Taylor and Burr 1997).

Fecundity:  A study by Taylor and Burr (1997) found spawned eggs to be spherical and translucent at <24h post-fertilization; asymmetrically surrounded by a dense mat of chorionic filaments, making them extremely adhesive; eggs averaged 1.95 mm in diameter at <24h post-fertilization and hatched in 9-11 days when incubated at 25 ± 2 C; clutch size ranged from 7-30 with an average of 20.2; ≥ 2 clutches per season; mean mass of most developed ripe ovum 6.72µg; mean diameter of most developed (ripe) ovum 2.74 mm.

Age at maturation:  Females capable of spawning at 1 year of age (26 mm SL for females) (Taylor and Burr 1997).

Migration:

Growth and Population structure:  Mean total length of hatchlings 6.1 mm (Taylor and Burr 1997). Becker (1983) notes five specimens collected from the Wisconsin River (Iowa County) in June, were age II and 47-55 mm long, and had the following estimated lengths at the annuli: at 1, 30 mm; at 2, 49 mm.

Longevity: At least 2 years (Taylor and Burr 1997); Becker (1983) notes that few individuals reach age 3.

Food habits: Invertivore (Simon 1999). Feeds heavily on terrestrial insects at surface of water (Forbes and Richardson 1920); Gunning and Lewis (1955) reported F. dispar feeding on snails, water fleas (Hydrachnida), chironomids and various other dipterans, filamentous algae.

Phylogeny and morphologically similar fishes

Subgenus Zygonectes (Wiley 1986). Formerly considered subspecies of F. notti (Brown 1958). Griffith (1974), Wiley and Hall (1975), and Wiley (1977) recognized F. dispar as distinct species (Wiley 1980). Wiley (1977, 1986) hypothesized that F. dispar is closest related to F. blairae.

Personal comment by Robert C. Cashner indicates Fundulus dispar is sister to, or conspecific with Fundulus blairae (Boschung and Mayden 2004).

Fundulus dispar differs from F. chrysotus, F. notatus, and F. olivaceus in having a dark suborbital bar and lacks the dark broad lateral stripe found in the last two species. Fundulus blairae, both male and female, differ from male F. dispar in lacking vertical stripes on the side. Female F. blairae differ from female F. dispar in having numerous dashes and less discrete melanophore development between the stripes on the body (Boschung and Mayden 2004). Gambusia affinis is similar to F. dispar in body shape and that it also has a dark patch under the eye, but G. affinis lacks horizontal streaks or vertical bars on the sides, has only 8 anal fin rays, and males have the anal fin modified into a rod-like gonapodium (Etnier and Starnes 1993).

Host Records

Commercial or Environmental Importance

References

Agassiz, L. 1854. Notice of a collection of fishes from the southern bend of the Tennessee River, in the state of Alabama. Amer. J. Sci. Arts, 2^nd ser. 17(51):353-369.

Balon, E. K. 1981. Additions and amendments to the classification of reproductive styles in fishes. Environmental Biology of Fishes. 6:377-389.

Becker, G. C. 1983. Fishes of Wisconsin. The University of Wisconsin Press, Madison, 1052 pp.

Boschung, H. T., Jr., and R. L. Mayden. 2004. Fishes of Alabama. Smithsonian Books, Washington, 736 pp.

Brown, J. L. 1958. Geographic variation in southeastern populations of the Cyprinodont fish Fundulus notti (Agassiz). American Midland Naturalist 59(2):477-488.

Etnier, D. A., and W. C. Starnes. 1993. The Fishes of Tennessee. The University of Tennessee Press, Knoxville, 681 pp.

Forbes, S. A., and R. E. Richardson. 1920 The Fishes of Illinois, 2^nd ed. Illinois Nat. Hist. Surv. Bull. 3:1-357.

Griffith, R. W. 1974. Environment and salinity tolerance in the genus Fundulus. Copeia 1974(2):319-331.

Gunning, G. E., and W. M. Lewis. 1955. The fish population of a spring-fed swamp in the Mississippi bottoms of southern Illinois. Ecology 36(4):552-558.

Page, L. M., and B. M. Burr. 1991. A Field Guide to Freshwater Fishes of North America north of Mexico. Houghton Mifflin Company, Boston, 432 pp.

Pflieger, W. L. 1975. Fishes of Missouri. Missouri Department of Conservation, 343 pp.

Ross, S. T. 2001. The Inland Fishes of Mississippi. University Press of Mississippi, Jackson, 624 pp.

Simon, T. P. 1999. Assessing the sustainability and biological integrity of water resources using fish communities. CRC Press. Boca Raton; London; New York; Washington.

Smith, P. W. 1979. The Fishes of Illinois. University of Illinois Press, Urbana, 314 pp.

Taylor, C. A., and B. M. Burr. 1997. Reproductive biology of the northern starhead topminnow, Fundulus dispar (Osteichthyes: Fundulidae), with a review of data for freshwater members of the genus. American Midland Naturalist 137(1):151-164.

Warren, L. W., Jr., B. M. Burr, S. J. Walsh, H. L. Bart, Jr., R. C. Cashner, D. A. Etnier, B. J. Freeman, B. R. Kuhajda, R. L. Mayden, H. W. Robison, S. T. Ross, and W. C. Starnes. 2000. Diversity, Distribution, and Conservation status of the native freshwater fishes of the southern United States. Fisheries, Conservation. 25(10):7-29.

Wiley, E. O. and D. D. Hall. 1975. Fundulus blairae, a new species of the Fundulus notti complex (Teleostei: Cyprinodontidae). Amer. Mus. Novit. 2577:1-13.

Wiley, E. O. 1977. The phylogeny and systematics of the Fundulus notti species group (Teleostei: Cyprinodontidae). Occas. Pap. Mus. Nat. Hist. Univ. Kans. 66:1-31.

Wiley, E. O. 1980. Fundulus dispar (Agassiz), northern starhead topminnow. pp. 514 in D. S. Lee, et al. Atlas of North American Freshwater Fishes. N. C. State Mus. Nat. Hist., Raliegh, 854 pp.

Wiley, E. O. 1986. A study of the evolutionary relationships of Fundulus topminnows (Teleostei: Fundulidae). Amer. Zool. 26:121-130.