The term fish refers to a number of aquatic and marine animals ranging from jawless creatures with cartilaginous skeletons to sharks and bony, ray-finned fishes. They share backbones, fins and gills, and are typically described as cold-blooded. All but one (the chestnut lamprey) of the fish species of Saskatchewan are bony fishes. Fishes first appear in the fossil record in the late Cambrian period; but the first ray-finned fishes (in the form of sturgeon-like fish) do not appear until the late Silurian, with most present forms not being found until the Eocene. Presently, there are 58 species of fishes from 15 families considered native to Saskatchewan (see Table FOS-1), with 11 extant species of exotic fishes from three families which have invaded or been introduced (see Table FOS-2). Most familiar are the larger-bodied fishes such as northern pike, walleye or lake trout; but more than half of the species are smaller, many of which are members of the minnow family (see Figure FOS-1). The most recent addition to Saskatchewan’s list of native fishes is the prairie minnow, which was discovered in Rock Creek in 2003.
Initial colonization is thought to have followed closely upon glacial recedence and to have followed three main routes: southern entry via the Missouri and Red River systems (the Mississippi and Montana refugia); and northern and eastern entry from Arctic refugia via the Mackenzie, Churchill and Nelson drainages (the Atlantic, Beringia and Nahanni refugia). This contributed to the cold water assemblage still present in many of the northern lakes. Some freshwater-adapted marine species, such as the deepwater sculpin, colonized during this period of marine inundation. Further colonization occurred as waters warmed, ecosystem diversity increased, and organisms dispersed from their more southern glacial refugia. Individuals travelled through connected waters or where floods formed new connections. It is through these mechanisms that the majority of the aquatic biota of Saskatchewan was established. There is speculation that the channel catfish and rock bass may have immigrated more recently: this supposition arises as they are currently expanding their range in Saskatchewan, and confirmed collections are restricted to the past half-century.
The majority of Saskatchewan’s fishes are spring spawners, although a number of the salmonids are fall spawners whose eggs over-winter before hatching in spring. The diet of fishes ranges from plankton to other fishes, with the adult lamprey perhaps being strangest in attaching to other fish and consuming both body fluid and tissue through its sucker mouth. The rarest native fishes appear to be the central mudminnow (Carrot River drainage), mountain sucker (headwaters of the Frenchman River), hybognathid minnows and stonecat (Frenchman and Assiniboine Rivers), and shortjaw cisco (Reindeer Lake and Lake Athabasca). The shortjaw cisco is listed as a threatened species, and the status of both the lake sturgeon and bigmouth buffalo is under review. Having only been found once in Saskatchewan, the central mudminnow was thought to be an accidentally occurring species; it was found again during a survey in 2004. Exotic fishes are species intentionally and officially introduced to Saskatchewan, regardless of their capacity to establish (many are reintroduced as populations wane). There are also fishes which have invaded and established after an intentional or accidental introduction elsewhere in North America.
American eel, Arctic char, Atlantic salmon, brook trout, brown trout, coho salmon, cutthroat trout, grass carp, kokanee, largemouth bass, rainbow trout, and smallmouth bass have been introduced by various provincial, federal, and private agencies. Each of these introductions was deemed successful, at least in terms of initial adult survival. Several of these species did not establish breeding populations and may no longer be extant. All of the grass carp currently stocked in Saskatchewan are effectively sterile (triploid) animals. All attempts to introduce black crappie, bluegill, rainbow smelt, and white crappie have been unsuccessful. Two types of hybrid fish have been, and continue to be, stocked by the province: the splake and the tiger trout. The common carp invaded and became established in Saskatchewan after its introduction to North America; records indicate an invasion prior to 1955.
There are several species for which there is insufficient evidence to determine if an established population exists. Two dead freshwater drum specimens were taken from the banks of Swift Current Creek in 1953. Nine western silvery minnows were collected from Tobin Lake in 1966 during a survey by the Royal Ontario Museum. No other confirmed specimens of this species have been taken from Saskatchewan waters. Fish taken from the Frenchman River, previously identified as western silvery minnows, have been determined to be brassy minnows upon re-examination of the collections. At various times goldfish, piranha, and oscar have been reported; most are found in sloughs, dugouts, and storm retention ponds. Undoubtedly, there have been other unrecorded instances of species once resident to aquaria being “stocked” to Saskatchewan’s waters.
In the future, climate changes may lead to an expansion in the range of some species and to the restriction or extirpation of others: for example, warm water fish such as channel catfish, largemouth bass and common carp may extend their ranges; but cold water species such as lake trout may be extirpated from the edges of their range. The recent (post-1940) loss of some lake trout populations from the more southerly portions of their former range in Saskatchewan has been attributed to over-harvest; however post-glacial climatic warming and isolation of watersheds through isostatic rebound may be at the root of these animals’ susceptibility to extirpation. Aquatic biota tend to be more vulnerable to extirpation since they are islandized by topography and further confined to river corridors for movement. These restricted corridors may be rendered temporarily or more permanently impassable due to man-made structures, unsuitable flows, depths or temperatures, and other obstacles such as beaver dams.