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Description

While thawing, the glaciers of Antarctica created an abundance of meltwater streams that now feed countless kilometres of freshwater ecosystems. At first nothing more than insect larvae and some crustaceans called these new environments home, but eventually fish entered the equation and quickly dominated.

One group of these fish were salmonids coming from South American coasts, descendants of invasive species such as the brown trout. They weren't the first, but they were much better at filling a lot of niches than the native Nothotenioids, which lacked hemoglobin and swim bladders.

And so they almost outcompeted these to extinction, and diversified into several genera classified roughly in three distinct groups: Helaks, Helerrets, and Valhallaks.
Most of the Helaks species are amongst the largest predators of the continent, and the Golden Helaks (Gjollsalmo fulgens) is the largest of them all, measuring up to 2 meters (7ft) long and more than 100kg (250lb) in weight. They're apex predators, using their size to block scape routes for prey fish of any size and swallowing them whole, preventing them from scaping thanks to its huge backwards facing teeth. They're also known to eat crustaceans and even birds that venture too deep into the water. They live in every waterway across Antarctica, with the adults being confined to the deeper canals and lakes.

Helerrets are the most common salmonids that can be found in the rivers, lakes and wetlands of the continent. These medium sized predators mainly feed on the abundance of mollusks and other hard shelled invertebrates, as well as smaller vertebrates occasionally. This diet is enabled by their strong jaws, combined with blunt teeth that can crack open the shells of most freshwater invertebrates in their habitats. They're also the only Antarctic salmonids that retain the anadromous habits of its ancestors, living in freshwater but migrating to coastal waters to reproduce and release their young into the rich waters of the Southern Ocean.

The Bullheart Helerret (Slidrsalmo oatensis) in particular is native to the drainage basins that flow into Oates bay, where members of this species comes to spawn.

Valhallaks are a group of salmonids with remarkable sexual dimorphism compared to their close relatives. They are typically found in shallow rivers all across the continent, where they feed on invertebrates and vegetation. Although not as common as Helerrets, they are abundant, specially in alpine streams and lakes during the end of the summer, where they come to spawn, away from predators so their eggs are protected by ice during the winter.

The Bearded Valhallaks (Valholsalmo auratops) specifically is endemic to the Vostok river drainage basin, which originates in Vostok Lake where they reproduce.

Description

While thawing, the glaciers of Antarctica created an abundance of meltwater streams that now feed countless kilometres of freshwater ecosystems. At first nothing more than insect larvae and some crustaceans called these new environments home, but eventually fish entered the equation and quickly dominated.

One group of these fish were salmonids coming from South American coasts, descendants of invasive species such as the brown trout. They weren't the first, but they were much better at filling a lot of niches than the native Nothotenioids, which lacked hemoglobin and swim bladders.

And so they almost outcompeted these to extinction, and diversified into several genera classified roughly in three distinct groups: Helaks, Helerrets, and Valhallaks.
Most of the Helaks species are amongst the largest predators of the continent, and the Golden Helaks (Gjollsalmo fulgens) is the largest of them all, measuring up to 2 meters (7ft) long and more than 100kg (250lb) in weight. They're apex predators, using their size to block scape routes for prey fish of any size and swallowing them whole, preventing them from scaping thanks to its huge backwards facing teeth. They're also known to eat crustaceans and even birds that venture too deep into the water. They live in every waterway across Antarctica, with the adults being confined to the deeper canals and lakes.

Helerrets are the most common salmonids that can be found in the rivers, lakes and wetlands of the continent. These medium sized predators mainly feed on the abundance of mollusks and other hard shelled invertebrates, as well as smaller vertebrates occasionally. This diet is enabled by their strong jaws, combined with blunt teeth that can crack open the shells of most freshwater invertebrates in their habitats. They're also the only Antarctic salmonids that retain the anadromous habits of its ancestors, living in freshwater but migrating to coastal waters to reproduce and release their young into the rich waters of the Southern Ocean.

The Bullheart Helerret (Slidrsalmo oatensis) in particular is native to the drainage basins that flow into Oates bay, where members of this species comes to spawn.

Valhallaks are a group of salmonids with remarkable sexual dimorphism compared to their close relatives. They are typically found in shallow rivers all across the continent, where they feed on invertebrates and vegetation. Although not as common as Helerrets, they are abundant, specially in alpine streams and lakes during the end of the summer, where they come to spawn, away from predators so their eggs are protected by ice during the winter.

The Bearded Valhallaks (Valholsalmo auratops) specifically is endemic to the Vostok river drainage basin, which originates in Vostok Lake where they reproduce.