Lox are one of only three creatures in Valheim you can currently tame, and the only one not based on a real-world animal.
This giant reptile is the size of a pachyderm, and looks like a cross between a buffalo and a Gorn from Star Trek, with what may or may not be porcupine spikes on its back.
(And despite the name, one of the few animals lox doesn't seem to be related to is the salmon.)
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How to tame lox in Valheim
First, stock up on plenty of their favourite foods — for lox this is barley, cloudberries, and flax. Fortunately these happen to be the three native plants in the Plains biome, which is the only area where the lox can spawn.
Ensure that the lox isn't alerted to your presence (or that of other players or enemies) and throw some food towards it.
Despite the lox's size, and the creatures of the Plains biome generally being an aggressive bunch, this is actually surprisingly easy. Lox have the worst vision and hearing of any creature in the game, so sneaking up on one — whether to attack it or offer it an overture of friendship — isn't very difficult.
Once the lox begins to eat, look for the yellow hearts above its head indicating that it's becoming acclimatized to your presence. If you get close enough for its stats to appear on your screen, you should see a percentage based trust metre as well. When that metre hits 100% (which will take multiple feedings), you've tamed a lox.
Building a lox pen
As with boars, you can ensure your tamed lox stays where you can keep an eye on it by building a pen for it.
Due to the lox's impressive blunt damage attacks, you're recommended to build your lox pen out of stone rather than wood. They can batter rocks too if they put their minds to it, but even a calm lox can damage its wooden enclosure.
Can you breed lox?
At the time of writing, the ability to breed lox in Valheim has not yet been implemented.
This means that you can't really effectively farm them at this point. You can feed them when they're hungry and keep them safe from attack in a shelter, but that's about it. They neither function as farm animals like tamed boars, nor as loyal companions like tamed wolves.
The only real advantage to taming lox at this point is that it keeps them from attacking your buildings and even your boats. Given the creature's aforementioned ability to go through wood like a hot knife through butter, this alone can make taming and penning them worth considering.
However, given that the game is still in Early Access, it's likely that a bigger role for your tame lox is coming at some point.