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Montana Field Guides

Brook Stickleback - Culaea inconstans

Potential Species of Concern
Native/Non-native Species
(depends on location or taxa)

Global Rank: G5
State Rank: S4
(see State Rank Reason below)

Agency Status

External Links

State Rank Reason (see State Rank above)
The brook stickleback is currently ranked an S4 in Montana and is considered a potential species of concern. While this species is apparently secure, it may be quite rare in parts of its range, and/or suspected to be declining.
  • Details on Status Ranking and Review
    Brook Stickleback (Culaea inconstans) Conservation Status Review
    Review Date = 04/08/2010
    View State Conservation Rank Criteria
    Population Size

    ScoreU - Unknown


    Range Extent

    ScoreF - 20,000-200,000 km squared (about 8,000-80,000 square miles)

    Comment109,381 square kilometers based on Natural Heritage Program range maps that appear on the Montana Field Guide

    Area of Occupancy

    ScoreE - 100-500 km squared (about 25,000-125,000 acres)

    Comment262 square kilometers based on Heritage Range Maps and occupancy of 1% of landscape by streams and occupancy of 24% of sites surveyed

    Long-term Trend

    ScoreE - Relatively Stable (±25% change)

    CommentEven though they have been impacted by grazing, exotic species, and some dewatering, prairie streams have probably been pretty stable in terms of water etc. since the arrival of Europeans within +/-25%

    Short-term Trend

    ScoreE - Stable. Population, range, area occupied, and/or number or condition of occurrences unchanged or remaining within ±10% fluctuation

    CommentSince 1999, prairie fish surveys do not suggest decline as indicated by distribution data although this is not as sensitive to detecting decline as regular monitoring of a network of sites. The recent surveys have expanded their known range, but their actual range hasn't changed too much with the exception of introductions into new areas (e.g., Swan River, Pablo Reservoir, and areas along Yellowstone River, Jocko River, and Milk River).


    ScoreF - Widespread, low-severity threat. Threat is of low severity but affects (or would affect) most or a significant portion of the population or area.

    CommentIntensive agriculture, overgrazing, road crossings, dams, and exotic species (Northern Pike in particular) all represent threats.

    SeverityLow - Low but nontrivial reduction of species population or reversible degradation or reduction of habitat in area affected, with recovery expected in 10-50 years.

    CommentSpecies is capable of recovering quickly if suitable habitat is available. Perhaps the majority of prairie streams affected by intensive agriculture are capable of recovering to the point of supporting populations within 50 years.

    ScopeModerate - 20-60% of total population or area affected

    CommentOne half of Brook Stickleback range is subject to the presence of Northern Pike. Intensive agriculture probably threatens the species in 20% of its Montana Range. Intensive grazing is much more patchy, perhaps 5% of species range in Montana.

    ImmediacyModerate - Threat is likely to be operational within 2-5 years.


    Intrinsic Vulnerability

    ScoreC - Not Intrinsically Vulnerable. Species matures quickly, reproduces frequently, and/or has high fecundity such that populations recover quickly (< 5 years or 2 generations) from decreases in abundance; or species has high dispersal capability such that extirpated populations soon become reestablished through natural recolonization (unaided by humans).

    CommentLongevity of 3-4 years

    Environmental Specificity

    ScoreB - Narrow. Specialist. Specific habitat(s) or other abiotic and/or biotic factors (see above) are used or required by the Element, but these key requirements are common and within the generalized range of the species within the area of interest.

    CommentPresent in a variety of prairie stream sizes and substrates, but are dependent on clearer streams and macrophytes for nesting.

    Raw Conservation Status Score

    Score 3.5 – 0.0 – 0.0 – 0.0 = 3.5

General Description
The brook stickleback is unique among Montana's fishes in its appearance. This species is native east of the Continental Divide in northeastern Montana. Sticklebacks live in slow streams and lakes with submerged plants. They are spring spawners that build a nest from pieces of vegetation they glue together with a special kidney secretion. Sticklebacks feed on small crustaceans and insects and can reach a length of about 3 inches. They provide some food for other predatory fishes.

Diagnostic Characteristics
Brook sticklebacks are olive-green with mottling or light spots on the sides; the undersides are light yellow to silver. During breeding season the males are black with tinges of red; females may be dusky. The body is smooth, without scales, but with minute bony plates about the pores on the lateral line.

Species Range
Montana Range Range Descriptions

All Ranges
(Click legend blocks to view individual ranges)

Western Hemisphere Range


Range Comments
Native range includes the Missouri, Platte and Mississippi River drainages, from Canada, Montana and North Dakota south Dakota and northern Iowa; Mississippi River not all the way downstream to the mouth of Missouri River upstream to Illinois and Michigan. In Montana, this species is found east of the continental divide in streams of the Northern Prairies and Northwestern Great Plains Ecoregions. It has been introduced upstream in the Yellowstone River basin and the west side of the divide.

Observations in Montana Natural Heritage Program Database
Number of Observations: 822

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Brook sticklebacks are associated with dense vegetation in slow, clear streams and shallow lakes.

Food Habits
This species feeds on almost any aquatic invertebrate that is available. Scuds, water fleas, midges, and very small fishes have been found in their stomachs.

Reproductive Characteristics
Brook sticklebacks spawn May through June. The male builds a nest from vegetation and lures one or more females in to deposit eggs. Incubation is for 8 days at 60 degrees F.

  • Additional ReferencesLegend:   View Online Publication
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    • Barfoot, C.A. 1993. Longitudinal distribution of fishes and habitat in Little Beaver Creek, Montana. M.Sc. Thesis. Bozeman, MT: Montana State University. 66 p.
    • Barfoot, C.A. and R.G. White. 1999. Fish assemblages and habitat relationships in a small northern Great Plains stream. The Prairie Naturalist 31(2):87-107.
    • Burford, D.D. 2005. An assessment of culverts of fish passage barriers in a Montana drainage using a multi-tiered approach. M.Sc. Thesis. Bozeman, MT: Montana State University. 50 p.
    • Duncan, M.B. 2019. Distributions, abundances, and movements of small, nongame fishes in a large Great Plains river network. Ph.D. Dissertation. Bozeman, MT: Montana State University. 255 p.
    • Hendricks, P., S. Lenard, D.M. Stagliano, and B.A. Maxell. 2013. Baseline nongame wildlife surveys on the Fort Peck Indian Reservation. Report to the Assiniboine and Sioux Tribes of the Fort Peck Indian Reservation. Montana Natural Heritage Program, Helena, MT. 83 p.
    • Rosenthal, L.R. 2007. Evaluation of distribution and fish passage in relation to road culverts in two eastern Montana prairie streams. M.Sc. Thesis. Bozeman, MT: Montana State University. 78 p.
    • Stash, S.W. 2001. Distribution, relative abundance, and habitat associations of Milk River fishes related to irrigation diversion dams. M.Sc. Thesis. Bozeman, MT: Montana State University. 82 p.
    • Stringer, A.L. 2018. Status of Northern Pearl Dace and chrosomid dace in prairie streams of Montana. M.Sc. Thesis. Bozeman, MT: Montana State University. 150 p.
    • Wuellner, M.R. 2007. Influence of reach and watershed characteristics on fish distributions in small streams of eastern Montana. M.Sc. Thesis. Bozeman, MT: Montana State University. 80 p.
    • Young, B.A., T.L. Welker, M.L. Wildhaber, C.R. Berry, and D. Scarnecchia (eds). 1997. Population structure and habitat use of benthic fishes along the Missouri and Lower Yellowstone Rivers. 1997 Annual report of Missouri River Benthic Fish Study PD-95-5832 to U.S. Army Corps of Engineers and U.S. Bureau of Reclamation. 207 p.
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Citation for data on this website:
Brook Stickleback — Culaea inconstans.  Montana Field Guide.  .  Retrieved on , from