Trout refers to a number of freshwater species as well as anadromous fish that belong to the family Salmonidae, the only surviving family of the order Salmoniformes. The family also includes close cousins like salmon, char, whitefish, and other relatives.
These fish provide important ecological functions by being an integral part of the food chain. Trout are natural predators to aquatic invertebrates, especially insects and some amphibians, like tadpoles. In turn, they make up the food that birds feed on, like the kingfisher, and mammals like bears, raccoons, and beavers. Humans prize these fish for their sports and food value, and these trout are often raised in hatcheries for anglers and diners.
Trout that live in varying environments can have very different colors and patterns, which are used as camouflage. A trout which has recently swum upstream from the sea can seem silver-colored while the same species living in a stream or lake may have brighter coloration and pronounced patterns. Therefore, it is impossible to define a single, consistent pattern and coloration for a specific breed or species of trout.
Table of Contents
Trout belong to the subfamily Salmoninae and occupy three of the seven living genera: Salmo, Oncorhynchus, and Salvelinus.
Many members of the genus Salmo are commonly known as “Atlantic trout.” Some famous members include the brown trout and Adriatic trout.
Scientific name: Salmo trutta
Brown trout comes in a range of coppery brown and orange colors. The belly of the brown trout is yellowish-orange, though the orange is less vivid than that found on the brook trout. Their sides and gills are covered by black spots.
Brown trout that are living in the sea are silver in color and a dark back. Those living in lakes also have a silvery color, though they may have coppery shades with red and black spots, surrounded by pale or white halos.
Brown trout live most of their lives in salty, brackish water but will migrate every year to freshwater sources to breed.
Scientific name: Salmo obtusirostris
Also known as the softmouth trout, this endangered trout can be differentiated from other types by its elongated mouth. Adriatic trout has small, fleshy lips, relatively large scales and is generally green with red and black dots. Unlike the brown trout of the Adriatic sea, this fish does not have any vertical stripes.
Adriatic trout prefer to live in wide and deep rivers. These fish are threatened due to excessive damming, overfishing and hybridization with other species.
Scientific name: Salmo marmoratus
As its name suggests, the marble trout has a distinctive marble color pattern and a high growth capacity. The vividness of its color significantly depends on its immediate surroundings. Some marble trout have red spots around the lateral line that merge with its marbled pigmentation.
This trout is found in some rivers and basins of the Adriatic Sea, and mainly inhabits the water bodies in Italy, Slovenia, Croatia, and Bosnia-Herzegovina. They were believed to be the only native trout in the region before the introduction of brown trout in its region. Because of hybridization, the uniquely patterned marble trout has become one of the most endangered freshwater species.
Scientific name: Salmo letnica
The taxonomical status of the Ohrid trout is controversial as it is believed to be part of the complex brown trout family. The very rare fish is native to the Ohrid Lake in the Republic of Macedonia; however, it was successfully translocated to various other regions of Europe and the United States.
The trout has four intralacustrine forms that are differentiated by their different breeding areas and breeding times. These forms include Salmo balcanicus, Salmo lumi, Salmo aphelios, and Salmo letnica.
Scientific name: Salmo ischchan
The trout is an endemic species of Armenia’s Lake Sevan, known as Ishkhan in Armenian. It is also related to the brown trout. The trout’s name translates literally into “duke”. Some believe it is named after Sevan because of its beautiful coloration that ranges from pinks to yellows, depending on the microclimate and its nutrition. It is also considered a delicacy in Armenia and the species has existed long before men.
The trout have been successfully translocated to the Issyk Kul lake in Kyrgyzstan and are also bred in hatcheries nowadays. Like the Ohrid trout, the Sevan trout also has four strains, based on their breeding area, time and growth rate. The forms are summer bakhtak (Salmo ischchan aestivalis), winter bakhtak (Salmo ischchan ischchan), bojak (Salmo ischchan danilewskii) and gegharkuni (Salmo ischchan gegarkuni).
The genus Oncorhynchus includes the subgenus Rhabdofario, which include Pacific trout, like the rainbow trout, golden trout, and cutthroat trout.
Scientific name: Oncorhynchus apache
The Apache trout has a golden-yellow-brown back and a golden belly. They have medium sized dark brown or black dorsal spots that are surrounded by a pale halo and black speckles on its dorsal fin and tail fin as well. Its eyes have a black spot on each side of the pupil making it seem like a black stripe is running across each eye. They also sometimes have a dark olive head and back. Some of the fish may have yellow to gold markings beneath their lower jaws as well.
The Apache trout can grow up to 24 inches in length and weigh up to 6 lbs, although it rarely grows past 10 inches and can reach up to 16 inches in its native waters. These trout are native to very cool and clean freshwater mountain streams but now have been introduced to other water bodies, since they have been declared endangered.
Scientific name: Oncorhynchus clarkia
The unfortunately-named Cutthroat trout are named so because of their distinctive, vivid reddish-orange coloration on their lower gill plate area makes it seem like their throats have been cut. The cutthroat trout has 14 subspecies, including the Bonneville cutthroat trout, Lahontan cutthroat trout, the Yellowstone cutthroat trout, and the Colorado River cutthroat trout. Most of these subspecies have widely different coloring from each other, but they can be identified by their spots and overall yellow and red coloration.
The cutthroat is native to the western United States which has rugged rocky terrains. The terrain isolated individual pods of cutthroat trouts and they evolved from encounters with various other trout in the area. This led to many different species of cutthroat, which have their own distinct habits and vary in size. For example, the Lahontan cutthroat is a record-breaker and can reach over 30 inches and weigh over 40 pounds.
Scientific name: Oncorhynchus mykiss
Adult freshwater rainbow trout exhibit a variety of beautiful metallic coloration. These trout have a broad reddish or pink lateral band on the lateral lines, a red gill cover and black spots. The caudal fin is only slightly forked and more square shaped than other trout. Young rainbow trout have dark vertical oval spots called parr marks, which are retained into adulthood on golden trout and redband forms.
The anadromous species are called steelhead and spend the majority of the days in the salty waters of the Pacific Ocean. These fish are silver, with the red lateral stripe almost gone, and have a more streamlined shape from other freshwater rainbow trout. These trout can grow up to 45 inches long, in contrast to freshwater species that typically only grow up to 12 inches. They swim upriver to spawn. Lake-dwelling rainbow fish are also almost completely silver in color.
These fish are aggressive fighters and jump out of the water when hooked. They are also stocked in streams and ponds because of their resilient ability to withstand situations that would kill most other species of trout.
Scientific name: Oncorhynchus mykiss aguabonita
The golden trout or the Californian golden trout is a subspecies of the rainbow trout. The golden trout has bright golden flanks with bright orange-red stripes running along the lateral lines. It also features about 10 dark vertical oval marks known as parr marks on each side. Its back and tail fin may sometimes be dark olive in color, and its dorsal, lateral and anal fin may have white edgings. It also has black dots on its dorsal side and tail fin.
Adult golden trout grow up over 12 inches long and can weigh over 6 pounds. Like all trout, these fish prefer cold, high-altitude waters with a temperature not more than 60 °F. They feed on terrestrial insects and small shrimps.
Initial efforts to introduce the golden trout into other waters were largely unsuccessful, though the golden trout have been known to survive in Montana, Wyoming and some parts of Canada.
Scientific name: Oncorhynchus gilae
The Gila trout is a relative of the rainbow trout and has a yellowish, copper or golden coloration with fins that appear yellower than its body. Along its back, the golden coloration may darken to olive or greenish tone. Its body is scattered with small black spots.
Like the Apache trout, this species may also have black spots in the eye which make it appear as if their eyes are striped. This trout species has been found in many streams of New Mexico and Arizona.
The species is considered endangered because of competition, fishing, and hybridization with other trout species, like the rainbow trout. However, the biggest reason is habitat loss due to loss of shady trees and water flow caused by human fires, overgrazing and water diversion.
Genus Salvelinus includes chars or charrs with trout found in subgenera Baione and Salvelinus.
Scientific Name: Salvelinus fontinalis
Also known as the speckled trout or mud trout, brook trout are native to eastern North America and Canada, although they have been successfully introduced to other areas of North America as well as Europe and Asia, as well.
The brook trout is the state fish of 9 U.S. states and is considered the most beautiful trout species. The fish has dark olive green to brown coloration with vermiculation or marbled pattern of yellow shades across the flank, back, and dorsal fin. Bright red spots surrounded by pale blue halos also form on the flanks. Its belly and lower fins have a reddish color, and the fins are also edged in white. The bellies of the male become very red during spawning season.
Brook trout vary from 10 inches to 26 inches and weigh from 0.6 pounds to 6.61 pounds, though they can grow much bigger in size.
Brook trout inhabit very clean and cold waters, and hence, any change in the water quality can be observed from these trout. They also require a high level of oxygen to thrive.
Scientific Name: Salvelinus confluentus
The bull trout is a native of western and southwestern waters. Its name comes from the fact that it has an unusually large head and mouth. These fish have olive bodies and red and orange dots along their sides. They also have pale yellow dots on the back, and like most char species, have a white leading edge on the fins. They have very fine scales and no vermiculation on their body. During spawning season, males may exhibit a bright orange-red stripe on their bellies, but otherwise, their coloration remains the same.
Bull trout can grow quite massive in size, up to 41 inches in length and 32 pounds in weight. They can migrate to larger river tributaries or remain in tiny brooks all their lives. They can be distinguished from the brook trout by the presence of yellow, orange or pinkish colored spots on the back as opposed to red spots with blue halos on the brook trout. Their dorsal fins also do not have spots.
Scientific name: Salvelinus malma
Dolly Varden trout takes its name from a Charles Dickens’ novel, Barnaby Rudge, in which a character was in the habit of wearing very colorful clothes.
Dolly Varden trout is characterized by olive green or a gray back and sides, which fade to white towards the belly. The body is scattered with pale yellow or pinkish spots with some small red dots on the lower side. During spawning season, males will exhibit a bright orange streak along the belly, and their spots will become more vivid. Anadromous Dolly Varden may look silvery and do not have bright colors on their body.
Dolly Varden trout are very similar to bull trout, so much so that many people are unable to differentiate them.
Scientific name: Salvelinus namaycush
The lake trout is the largest type of trout native to the Great Lakes in northern North America. It is also known as grey trout, mackinaw, namaycush, lake charr, togue, touladi, siscowet, and paperbelly.
Unlike many other trout species, lake trout do not have a wide variety of colors on its body. It is mostly dark grey, green or purple in color, with light spots and a tawny belly with the typical white leading edges on the fins. However, it is one of the best fighter trout and hence a favorite of ice fishermen.
The largest lake trout caught was 50 inches long and weighed 102 pounds. Since it is a big fish, it also inhabits larger and deeper water bodies. They also do not usually eat insects, preferring to go after other fish, including trout, ciscoes, graylings, and whitefish.
Scientific Name: Salvelinus fontinalis × Salvelinus namaycush
The splake trout is a hybrid of a brook or speckled trout and lake trout, both belonging to genus Salvelinus. Its name itself is a portmanteau of the speckled and lake trout and may be used to refer to other such hybrids from as early as the 19th century.
Splake trout have a small fork in their tail courtesy of the lake trout. In contrast, brook trout have almost no fork in the tail and have a squarish tail. Splakes do not breed profusely and because of this, they are stocked in lakes to control the population.
Splakes have a faster growth rate than either of their parent species and can grow as much as 18 inches in just two years. Because of their large size, they are one of the preferred sport fish. They are also are not very smart and eagerly eat lures, making them very easy to catch.
Scientific Name: Salvelinus fontinalis timagamiensis
The aurora trout is named after the aurora borealis because of their beautiful and atypical color patterns. It is a variant of the brook trout but can be differentiated from it by the absence of yellow spots in the dorsal region and the red spots with blue halos, that brook trout are known for.
Aurora trout may have gradient colors, with a magenta hue in the back to a bright orange belly, especially in males. Adults usually weigh about 1 to 3 pounds, and the record is set at 6.44 pounds. Their life history is identical to that of brook trout.
The aurora trout occupied only two Canadian lakes, Whitepine and Whirligig, initially but were removed from the lake in the 1950s because of the risk of acid rain and translocated successfully to a dozen lakes in northeastern Ontario.
We should be grateful that there are so many surviving species of trout in the world. However, they are increasingly being threatened by pollution and overfishing, causing their numbers to dwindle. Although it is good to have fish in our diet, it is also important to contribute to causes that support the conservation of these trout.