Fundulus dispar

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The Starhead topminnow (Fundulus dispar) is a small freshwater fish native to the United States. It is listed as Least Concern globally by the IUCN, but some states rate it differently.

Distribution
- Found from the Ouachita River drainage in Louisiana and the Big Black River in Mississippi, north through the Mississippi River and Lake Michigan basins to southern Michigan and southern Wisconsin.
- In 2024, an isolated population was found in Iowa, the first since 1938.

Habitat
- Likes quiet, clear waters with lots of submerged vegetation.
- Lives in glacial lakes, vegetated floodplain lakes, swamps, and marshes. Spawning also happens among vegetation.

Description
- Back and upper sides are light olive tan; belly is lighter to yellowish.
- Red to brown lines run along the sides (usually 6–8 in females, 3–13 in males).
- A prominent teardrop-shaped dark blotch sits beneath the eye.
- Dorsal fin is positioned far back on the body.
- Length: about 1.8–2.2 inches (47–55 mm).
- 18–20 scales surround the tail area.
- A bright gold spot sits on the top of the head, with a smaller spot in front of the dorsal fin.

Diet
- Feeds on terrestrial and aquatic insects, crustaceans, mollusks, and aquatic vegetation.

Reproduction
- Spawning occurs from June to August.
- Reproduction happens best between 18.4°C and 29°C (65.3°F–84.2°F).
- Eggs are laid among vegetation or on the bottom and are not guarded by parents.
- Eggs are about 1.9 mm in diameter and hatch in about 9–11 days at around 25°C.
- A single female can lay up to about 33 eggs in a spawning event.

Threats and conservation
- Removal of aquatic vegetation and shoreline development reduce habitat and populations, especially where vegetation is removed (e.g., Fox River Chain of Lakes).
- Wisconsin counts it as endangered locally (state rank S2); globally it is considered apparently secure (G4), while Illinois lists it as threatened.