Fundulus sciadicus Cope, 1865
Basis for Listing
The Plains Topminnow (Fundulus sciadicus) has undergone a recent and drastic decline over most of the species’ range. One study identified 927 historic sites across its range from 1889-1999 and compiled survey data or revisited 667 of these from 2000-2010. However, the Plains Topminnow was found at only 28% of its former localities (Pasbrig et al. 2012). It was suspected to be extirpated in Iowa, until recent surveys found the species after a 70-year absence (Schmidt and Hrabik 2012). In Minnesota, it is restricted to the Rock River system in small prairie streams that are tributary to the Missouri River in Pipestone, Nobles, and Rock counties. The species has specialized habitat requirements, and its fragile habitat is subject to siltation drought, and groundwater depletion. Given its extreme rarity in the state, the Plains Topminnow was listed as a special concern species in Minnesota in 1984. At that time, information on distribution, abundance, preferred habitats, and life history was limited. In 2013, following the completion and analyses of targeted surveys, the status of the Plains Topminnow was elevated to threatened.
The Plains Topminnow is olive-brown in color on its back and sides, white below, and reaches a total length of 4.0-6.5 cm (1.6-2.6 in.). Its stout body has 34-36 scale rows and lacks the black bars that are characteristic of the more common Banded Killifish (Fundulus diaphanus). It has a small mouth with a projecting lower jaw, a broad head, and a single soft dorsal fin with 8-10 rays that lies slightly behind the front of the anal fin. Male Plains Topminnows have larger anal fins than females, red fin edges, blue speckles, and a gold stripe down their back. Topminnows are easily distinguished from true minnows by the far rear position of their dorsal fin, which begins behind the beginning of the anal fin.
Plains Topminnows are found in spring-fed pools and backwaters of clear to moderately turbid creeks and rivers that have a sand or rock bottom and a heavy growth of aquatic plants (Phillips, in preparation).
Biology / Life History
Little is known about the life history of the Plains Topminnow. It lives singly or in small schools near the surface of the water (Pflieger 1975). Both males and females mature in their second summer (age 1). Females deposit eggs on aquatic plants, and the eggs hatch in 8-20 days. Plains Topminnows live for up to four years and feed on seed shrimp (ostracods), small snails, larval midges and blackflies (Stribley and Stasiak 1982). Predators likely include larger fish such as bass (Micropterus spp.) as well as fish-eating birds.
Conservation / Management
The Plains Topminnow is one of the rarest inhabitants of Minnesota's southwestern prairie streams (Hatch et al. 2003). Water quality and quantity of streams in southwestern Minnesota need to be maintained at present levels, and efforts to minimize siltation should be encouraged. Research about this species' natural history is needed to support management and conservation.
One factor attributed to the decline of the Plains Topminnow in other states is the introduction of non-indigenous fish species such as the piscivorous Largemouth Bass (Micropterus salmoides) in reservoirs and impoundments and competition from Western Mosquitofish (Gambusia affinis), which remains in widespread use as a biological control for mosquitoes (Pasbrig et al. 2012). The Largemouth Bass is very rare in Minnesota habitats of the Plains Topminnow; however, Smallmouth Bass (M. dolomieu) were first detected in the Minnesota’s Missouri River drainage streams in 2012 and in several more sites in 2013 (Schmidt 2013). The topic of stocking game species needs to be addressed with neighboring states to protect both the Plains Topminnow and the federally endangered Topeka Shiner (Notropis topeka). There are no known populations of Western Mosquitofish established in Minnesota, but it does occur in Iowa and Wisconsin and is spreading northward.
Plains Topminnows have successfully been cultured in ponds, which may become a management consideration for reintroduction to recovered habitats that are free of detrimental non-indigenous species (Schumann et al. 2012).
Conservation Efforts in Minnesota
Fish surveys in the 1990s and 2000s increased the known number of locations of this species in Minnesota to at least 20 and the known number of rivers and tributaries to eight, all of which are within the Rock River system. The Plains Topminnow continues to be a target species for the Minnesota Biological Survey. Additional research needs for the species in Minnesota include life history studies, genetic analysis, identification of habitat guilds, and the determination of specific habitat impacts and stressors.
The recent inception of Minnesota’s Clean Water Legacy Program will eventually yield benefits to Plains Topminnow habitats through nutrient and sediment load reduction. The restoration and creation of off-channel habitat in the Missouri River basin as part of the Cooperative Restoration Initiative: Topeka Shiner Recovery in Southwest Minnesota project should benefit this species as well; the project began in 2015.