is grayish or olive green with a varying amount of indistinct mottling, but during the spawning season, males are nearly black and females have darker and lighter patches. This species grows to a maximum length of . Geographic distribution of species Culaea inconstans, commonly known as the brook stickleback, is a small fish (<87 mm) that occurs throughout the southern half of Canada and the northern part of the eastern United States. It is one of the smallest fishes in the region. Brackish water populations are uncommon but certainly exist. It extends down to the southern reaches of the Mississippi River – Great Lakes drainage basins. Populations also exist in Colorado and Nebraska to the west, and in Alberta, Manitoba, and Northwest Territory to the north. Though these are typically the native ranges of the brook stickleback, the species has been introduced to Alabama, Kentucky, Tennessee, northwestern Colorado, northeastern Utah and California, and even in parts of South Dakota and Washington State. Certain geographical distribution studies have found that certain populations may have been native in New Mexico and still exist today. Nebraska does have brook stickleback populations, but they are generally found in small streams in the northern portion of the state. The fish have been found in Nebraska since the early part of the nineteen hundreds. River drainages that sustain brook stickleback populations are the Loup, Middle Platt, Niobrara, and smaller distributions in the Lower Platte, Missouri River tributaries, North Platte, and South Platte. Though the species appears to have an abundant distribution across North America, the Nature Conservancy has declared the species to be a S3 (vulnerable) level. Reasons for the level of vulnerability could be due to increased dam construction, especially in the eastern United States. This can lead to a destruction of habitat, increase in silted waterways, alteration of stream nutrient transport, and damaged breeding grounds. Alteration of stream dynamics could also lead to a change in predator frequency, thus exposing the brook stickleback to unforeseen predators. Introduction in Europe The brook stickleback was introduced in upper drainage of the River Inn in Bavaria, and in the 1960s was accidentally introduced to alongside Micropterus species to Lake Lohjanjarvi in southern Finland and it has become established there. Ecology As with a large geographical distribution, this species also lives in a wide range of flowing water habitats. Waterways such as rivers, streams, floodwater streams and drainages,