In Argentina it is possible to find a variety of species, depending on the body of water you have chosen to practice fly fishing. In lagoons, lakes, rivers and in the Ocean, there are dozens of different species of trout, sharks, salmons and other smaller types of fish. Here, you can read about the more important sport species.

Rainbow Trout (Onchorhynchus mykiss)
Is there a more beautiful or popular fish? Depicted on corporate logos, ball caps and gas station signs, the rainbow trout is the ideal symbol, combining beauty and sport. The rainbow trout (Oncorhynchus mykiss) is favored by fly fishermen because of its beautiful coloration – for which it is named – and it’s fighting ability. Wild rainbow trout typically have olive-colored backs and tails that peppered with dark spots and silvery sides that look as if they’ve been painted with pink to crimson watercolors.
The rainbow trout is actually a member of the Pacific salmon family, and has been stocked on six continents. It can be found in freshwater streams, rivers and lakes, also in saltwater bays and open ocean as steelhead (the sea-run form of the fish, which returns to freshwater during the spawn). Trout seem to prefer moderately moving creeks and streams with plenty of cover and pools, although rainbows also do well in food-rich backcountry lakes and rivers.
The rainbows size relates generally to the size of the water they can be found in. Smaller creeks are usually home to smaller fish, while bigger rainbows inhabit bigger watersheds.. Generally speaking, a three-year-old rainbow trout in a general trout stream grows to 12 inches but can exceed 20 inches of food is abundant and water temperatures are mild and stable throughout the year.

Brown Trout
The brown trout (Salmo trutta morpha fario and S. trutta morpha lacustris) and the sea trout (S. trutta morpha trutta) are fish of the same species. But each is a horse of a different color, to mix fish and equine metaphors. They are distinguished chiefly by the fact that the brown trout is largely a freshwater fish, while the sea trout shows anadromous tendencies, migrating to the oceans for much of its life and returning to freshwater only to spawn. The brown trout is normally considered to be native to Europe and Asia but the natural distribution of the migratory forms may be, in fact, circumpolar. The fish is not considered to be endangered in any location although in some cases, individual stocks are under various degrees of stress mainly through habitat degradation, and artificial propagation leading to introgression.
Brown trout likes cold (though in comparison with other trout, this species has a somewhat higher temperature preference of about 60-65 °F, or 15.5-18.3 °C), well-oxygenated waters, especially large streams in mountainous areas. Cover is important to trout, and they are more likely to be found where there are submerged rocks, undercut banks, and overhanging vegetation.
The brown trout is a medium sized fish, growing to 9 lbs/20 kg or more in some localities although in most small rivers a mature weight of 1 kg (2 lb) is common.
Brown trout are active both by day and by night and are opportunistic feeders. While in fresh water, the diet will frequently include invertebrates from the streambed, small fish, frogs, and insects flying near the water's surface. The Brown’s penchant for insect larvae, pupae, nymphs and adult insects is what allows this trout to be a favored target for fly fishing.

Sea Run Brown Trout
The salmon….that isn’t a salmon. Brown trout (Salmo trutta L.) are one of the most widely distributed non-native fish introduced to Patagonia. They were first stocked in Tierra del Fuego by John Goodall in 1935. Shipped from Puerto Montt in Chile, 60,000 'salmo trutta' eggs survived the arduous journey to be planted on the Candelaria and McLennan rivers, both tributaries of the Rio Grande. These fish eventually found their way to the sea, attracted by the rich food supply located just off shore.
Today, sea-run brown trout complete a yearly migratory cycle just like atlantic salmon and other salmonids that also spawn in freshwater. Sea run browns remain in the river for a period of time which ranges between 1 and 4 years until their first migration to the sea, where they will feed and grow for about 6 months before their first return to freshwater, weighing approximately 6lbs. Researchers have found trout which have spawned as many as six or seven times. A trout that has completed 4 cycles of returning to freshwater can weigh over 20 lbs. The regularity with which these trout return to freshwater indicates that the fish face few threats. Regardless--catch and release fishing still rules the day.
Sea run trout are not geese, and they were not “supposed” to migrate really. The role of environmental factors versus genetics on the ‘decision’ of sea run trout to migrate is still unknown. While genetics likely play an underlying role in the development of migratory populations, studies of other fish species fail to differentiate genetically between resident and migratory individuals within a population, and in fact indicate that interbreeding often occurs between the migratory and resident individuals. In some rivers they migrate, in others they don’t. That is just the deal, but we are sure glad that the salmo trutta migrates on the Rio Grande and Rio Gallegos.

Freshwater dorado
The dorado is often described as a prehistoric salmon with the jaws of a pit bull terrier. You see that defenition a lot, because it is pretty accurate. The dorado are golden, they have a powerful set of jaws reminiscent of a dog, they are strong, and they jump. Pretty good recipe for a game fish isn’t it?
Dorado are hard-hitting, incredibly-strong, acrobatic fighters that has long been one of the most admired fish in South America; but it is almost completely unknown in the rest of the world. Outside of South America, the dorado suffers an identity crisis. Many anglers confuse this distinct gamefish with other species. Although the dorado’s body is reminiscent of the salmon, it is not at all related. The dorado does not die after spawning and never swims in the ocean. And while its common name is similar, the dorado is a freshwater gamefish and not to be confused with the saltwater “dolphin” fish (called 'el dorado' in many Spanish-speaking countries).
Dorado are exceptionally strong swimmers. They typically range in size from 5 to 10 pounds. In some fisheries, twenty pounders are common. The dorado’s intense, almost radiant, golden color is marked with holographic black horizontal stripes. This patterning, coupled with their powerful jaws and razor sharp teeth have earned the dorado the sobriquet “River Tiger” in Argentina. The dorado is a great jumper and a prodigious fighter. Once fooled with a fly or bait, their arm-wrenching strike is a testament to their aggressiveness and ferocity. As soon as an angler sets the hook, these wild leapers explode out of the water in a series of outrageous jumps.