steelhead [anadromous form], coastal rainbow

When rainbow trout leave lakes to spawn, their coloration becomes more intense: the pinkish stripe that is present on the sides of lake fish, along with the fins, turn a rich crimson color, and there is sometimes a red slash in the folds below the lower jaw. The belly and the lower sides turn gray, and spots on the sides and upper fins become bolder and more clearly delineated. Juvenile trout are olive-green along their back and silvery olive high on their sides. There are 8-13 oval-shaped marks along the sides, which may also have smaller dark spots along them. Blush-pink to yellowish markings occur along the lateral lines between the oval marks (McDowall, 1990).

For further identification guides, see Moyle (1976a); Scott and Crossman (1973); Wydoski and Whitney (1979); Morrow (1980); Eschmeyer et al. (1983); Page and Burr (1991); Behnke (1992). Behnke (1992) gave accounts and drawings for several subspecies. A commonly used named for this species is Salmo gairdnerii, sometimes given as S. gairdneri.

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Beneficial

Oncorhynchus mykiss has a high environmental impact in the Great Lakes.

Realized:
Rainbow trout and brown trout (Salmo trutta) were deemed at least partially responsible for the extirpation of Arctic grayling (Thymallus arcticus) in Michigan, its only known location in the Great Lakes Basin (Crawford 2001). Fausch (1988), Clark and Rose (1997), and numerous papers cited in both discussed several factors affecting competitive interactions between rainbow and brook trout (Salvelinus fontinalis), although the overall impact of this competition on brook trout is not well known (Crawford 2001). Reportedly, rainbow trout also drive nongame fishes such as suckers and northern pikeminnow (Ptychocheilus oregonensis) from feeding territories (Li, personal communication to P. Moyle in Moyle 1976a). Rainbow trout hybridize with other rarer trout species, thereby affecting their genetic integrity (Page and Burr 1991, Rinne and Minckley 1985) (see Potential Impacts for examples outside of the Great Lakes). Rainbow trout may also affect invertebrate populations. Feltmate and Williams (1989) found that the introduction of rainbow trout to an enclosure within a Great Lakes tributary in Ontario caused a 35% decline in stonefly abundance relative to areas without rainbow trout. Stonefly populations were adversely affected by both predation and disturbance, which led to emigration (Feltmate and Williams 1989).

Rainbow trout is an important aquaculture species produced in both land-based and water-based hatcheries. Although there are hundreds of land-based hatcheries and fewer than 15 freshwater cage farms in Canada (many of which are in Lake Huron), cage farms produce the majority of fish and rainbow trout are the numerically dominant species (Rooney and Podemski 2010). High volumes of aquaculture production have had adverse impacts in freshwater lakes. In a study of cage production in a freshwater lake in Ontario, Canada, Rooney and Podemski (2010) documented increases in ammonia and metal concentrations, such that Cu and Zn exceed sediment quality guidelines. Cage farms also release solid wastes, nitrogen, and phosphorus, which can cause increased algal blooms and decreased oxygen availability (Hamblin and Gale 2002). Such trends have already been documented in northern Lake Huron and nearby Lake Wolsey (Hamblin and Gale 2002). Additionally, stocking of hatchery rainbow trout in rivers has led to the introduction of whirling disease into open waters of approximately 20 states including, most recently, the Madison River and its tributaries in Montana (B. Nehring and R. White, personal communication). Both non-native and native salmonids are susceptible to the disease (Yoder 1972). In the Madison River, the disease has reduced the rainbow trout population by 90% (White, personal communication).

Crawford et al. (2001) pointed out that salmonids have the potential to alter the energy and nutrient cycles of the Great Lakes system through increased energy transfer between open water and streams/tributaries. This energy transfer includes the addition of nitrogen and phosphorus to tributaries through decaying salmonine carcasses, as well as the addition of salmon eggs and dead fish as a food source in streams (Ivan et al. 2011, Parmenter and Lamarra 1991, Rand et al. 1992). Rand et al. (1992) found that phosphorus released from salmon carcasses was responsible for >50% of the total phosphorus discharged in some Lake Ontario streams during parts of the spring. The presence of live salmonids may have an even greater effect on nutrients in streams through the excretion of ammonium and soluable reactive phosphorus and their mechanical disturbance of the stream bottom during spawning runs (Ivan et al. 2011, Tiegs et al. 2009).

Potential:
Rainbow trout have the potential to consume native fishes and compete with native salmonids (Page and Laird 1993). Introduced rainbow trout eat endangered humpback chub (Gila cypha) in the Little Colorado River and may exert a major negative effect on the population there (Marsh and Douglas 1997). Rainbow trout have been found to negatively affect Little Colorado spinedace (Lepidomeda vittata) through predation and by affecting spinedace behavior. The trout occupied undercut banks that the spinedace normally used for refuge. As a result, spinedace were displaced from preferred microhabitats and pushed into open water, making them vulnerable to predation (Blinn et al. 1993). Introduced predatory fishes, including the rainbow trout, are likely at least partially responsible for the decline of the Chiricahua leopard frog (Rana chiricahuensis) in southeastern Arizona (Rosen et al. 1995).

In California, rainbow trout have hybridized with Lahontan cutthroat trout (O. clarki henshawi), golden trout (O. aguabonita), and redband trout (O. mykiss subsp.) to the point that all three are included in the threatened trout management program of the California Department of Fish and Game (Behnke 1992, McAffee 1966b, Moyle 1976b). In the Lahontan drainage and various Rocky Mountain rivers, hybridization with rainbow trout has been a major factor in the decline of native cutthroat trout (O. clarkii henshawi) (McAffee 1966a). In fact, rainbow trout have replaced Lahontan cutthroat trout in many areas where the cutthroat is native and rainbow trout have been introduced (McAffee 1966b). For instance, introduced rainbow trout were likely partially responsible for the near-extinction of Lahontan cutthroat in Lake Tahoe in the 1940s (McAffee 1966b). Rainbow trout have been shown to hybridize with Westslope cutthroat trout (O. clarki lewisi) throughout the Flathead River system in Montana (Muhlfeld et al. 2009). Oncorhynchus clarkii lewisi hybridization with O. mykiss, and the resulting backcrossing to pure parent populations, has also resulted in strong introgression toward both populations in the Upper Oldman River, Alberta, Canada (Rasmussen et al. 2010). In Nevada, this species is also held responsible for the virtual extinction of Alvord cutthroat O. mykiss subsp. (Behnke 1992). In Arizona, the species has hybridized with native Gila trout (O. gilae) and Arizona trout (O. apache) (Minckley 1973, U.S. Fish and Wildlife Service 1979). The latter species is also known as the Apache trout and is considered a subspecies of O. gilae (i.e. O. g. apache).

There is little or no evidence to support that Oncorhynchus mykiss has significant socio-economic impacts in the Great Lakes.

Oncorhynchus mykiss has a high beneficial effect in the Great Lakes.

Realized:
Rainbow trout has been stocked as a recreational species in the Great Lakes since the 1800s and are currently stocked in all five lakes and Lake St. Clair (FWS/GLFC 2010, NYDEC 2011). The U.S. Fish and Wildlife Service (U.S. FWS 2006) estimated that nationally, every dollar spent on hatchery programs for rainbow trout returns over $36 of net economic value. One survey estimated the rainbow trout recreational fishery to be worth up to $12-14 million annually in Lake Erie, compared to a stocking cost of $600,000 (Kelch et al. 2006). Additionally, the global production of aquacultured rainbow trout has grown continuously, annually producing over 700,000 tons as of 2010 (FAO 2011).

Potential:
Eggs spawned by steelhead have been found to comprise an important part of the native brown trout diet in Great Lakes tributaries, but the effects of this consumption have yet to be understood (Ivan et al. 2011).

In New York, trout, including rainbow trout, shall not be bought and sold, excepting cases in which a hatchery permit is issued, as described under NY ECL § 11-1909. In Ohio, it is unlawful to take or possess rainbow trout less than 12 inches in length while on Lake Erie or its tributaries, including all streams in the entire drainage basin, excepting Cold Creek upstream of state route 2 located in Erie County, and Beaver Creek in Seneca County. It is also unlawful to take or possess rainbow trout less than twelve inches in length while on the Mad River or its tributaries (Ohio Admin. Code § 1501:31-13-09). In Michigan, rainbow trout is an approved species for aquaculture production (MCL § 286.875). In Wisconsin, rainbow trout is restricted as a nonnative fish species in the aquaculture industry, and therefore cannot be transported, possessed, transferred, or introduced without a permit (Wis. Admin Code § NR 40.05).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Biological
There are no known biological control methods for this species.

Physical
In streams and rivers, barriers can be constructed and natural barriers augmented to prevent upstream migration of trout and aid management and eradication efforts. In a report on a successful trout removal program involving a combination of piscicides (rotenone) for eradication and barriers for prevention of re-invasion, Lintermans and Raadik (2003) noted 3 key aspects of successful barriers: a 1.5 m or greater vertical drop; direction of water flow towards the middle in higher flows with no slower overland flow passing down the banks; and no deep pool below the barrier from which trout could jump. Rainbow trout often rely on spawning streams and small tributaries for reproduction, and removal of access to such streams could reduce or potentially eliminate populations in downstream bodies of water (Champion et al. 2002). The U.S. National Park Service uses physical removal through electrofishing to manage rainbow trout and brown trout populations that threaten native brook trout in Shenandoah National Park, Virginia (National Park Service 2011).

Chemical
Antimycin A is a registered piscicide in the US that is documented as highly effective against scaled fishes, including rainbow trout (Finlayson et al. 2002). Elimination of trout is achievable in a contact time of 2 hrs. at 5 µg/L (5 ppb), or in 1 hr. at 10 ppb (Finlayson et al. 2002, Gilderhus 1972). Antimycin is most effective in small streams, shallow ponds, and alpine lakes where there is ample mixing and an adequate contact time can be achieved (Finlayson et al. 2002, Gilderhus 1972). Antimycin does not seem to repel fish like rotenone does, and rapidly breaks down by hydrolysis in natural waters (Finlayson et al. 2002). Disadvantages of antimycin include increasing ineffectiveness in waters with higher pH (>8), streams with significant gradients (80-150 m elevation drop), and large lakes where good mixing and contact time cannot be established (Finlayson et al. 2002). Rotenone is also effective against rainbow trout, but at much higher concentrations, with 50 µg/L required to eliminate trout in a 2 hr. contact time (Finlayson et al. 2002, Gilderhus 1972). Antimycin may be preferred because of the lower dose required. Antimycin and rotenone are non-selective, and toxicity to other fishes and aquatic invertebrates will vary.

Lintermans and Raadik (2003) provide a detailed account of rainbow trout elimination programs using rotenone in order to protect fishes of the family Galaxiidae, conducted in two separate areas of Australia. In 1992, rainbow trout were removed from 2.4 km of Lees Creek, Australian Capital Territory using a 5% rotenone emulsion at concentrations of approximately 0.05 parts per million (ppm) (Lintermans and Raadik 2003). The creek was treated in 500 m sections, with 300-350 mL of rotenone added over a 15-minute period to each section, and with mesh stop nets placed after each section to prevent downstream reinvasion of trout (Lintermans and Raadik 2003). An oxidant (350-500 g potassium permanganate) was added to the stream when rotenone reached the downstream limit of treatment sections to remove the toxicant (Lintermans and Raadik 2003). To prevent trout reinvasion of the treated area, a downstream weir was augmented with a heavy steel grill to present a 1.75 m vertical barrier (Lintermans and Raadik 2003). Complete eradication was accomplished at the Lees Creek site, and despite heavy impacts on aquatic macroinvertebrates, benthic macroinvertebrates remained in significant numbers (Lintermans and Raadik 2003). In 1995, a total of 20 km of stream length (7 different streams) was treated in Victoria, with a total of 60 L rotenone used, neutralized with 1100 kg of potassium permanganate, and with rotenone volumes ranging from 0.3 to 0.5 L per 100 m of stream (Lintermans and Raadik 2003). Areas in which trout and galaxiids overlapped were not treated with piscicides; they were instead intensively electrofished to more selectively remove rainbow trout (Lintermans and Raadik 2003).

The effects of combinations of management chemicals and other toxicants, whether intentional or unintentional, should be understood before pursuing chemical treatment options. Boogaard et al. (2003) found that the lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and 2’,5-dichloro-4’-nitrosalicylanilide (niclosamide) demonstrate additive toxicity when combined, with rainbow trout demonstrating 12h LC50s of 8.40-10.6 mg/L in response to treatments of TFM and 5.00-5.05 mg/L in response to treatments of a TFM/1% niclosamide combination in lab tests (Boogaard et al. 2003). In another study on cumulative toxicity, combinations of niclosamide and TFM with contaminants common in the Great Lakes (pesticides, heavy metals, industrial organics, phosphorus, and sediments) were found to be mostly additive in toxicity to rainbow trout, and one combination of TFM, Delnav, and malathion was synergistic, with toxicity magnified 7.9 times (Marking and Bills 1985). This highlights the need for managers to conduct on-site toxicity testing and to give serious consideration to determining the total toxic burden to which organisms may be exposed when using chemical treatments (Marking and Bills 1985).

Increasing CO2 concentrations, either by bubbling pressurized gas directly into water or by the addition of sodium bicarbonate (NaHCO3) has been used to sedate fishes with minimal residual toxicity, and is a potential method of harvesting fish for removal, though maintaining adequate CO2 concentrations may be difficult in large/natural water bodies (Clearwater et al. 2008). Laboratory trials demonstrated a combination of pH 6.5 and 642 mg/L NaHCO3 was the most effective treatment for rainbow trout (Clearwater et al. 2008). CO2 is approved only for use as an anaesthetic for cold, cool, and warm water fishes in the US. It is not approved for use as euthanasia (Clearwater et al. 2008).

It should be noted that chemical treatment will often lead to non-target kills, and so all options for management of a species should be adequately studied before a decision is made to use piscicides or other chemicals. Potential effects on non-target plants and organisms, including macroinvertebrates and other fishes, should always be deliberately evaluated and analyzed. Other non-selective alterations of water quality, such as reducing dissolved oxygen levels or altering pH, could also have a deleterious impact on native fish, invertebrates, and other fauna or flora, and their potential harmful effects should therefore be evaluated thoroughly.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.