Tamable using fish baskets from aberration. They seem to flee from the baskets once placed. It is a good strategy to pen then in with fence foundations and walls, or kite them to a pen. Place your basket on the other side of the wall and catch.
What I usually do is go through the lake and harpoon kill any that are 1.4x or less. Then I set traps and punch one of them, it'll grab the aggro from the others. Now you have 5 angry fish coming at you and your line of baskets.
The moment one of them is within range, just grab them in the basket line.
Wearing flak or riot gear is suggested but not necessary since 80% of the lake fish are dead and the remaining 20% won't deal too much damage
You don't need to build a pen to tame, I just tamed my first thanks to the tips on here. Just wait and check the traps that have salmon near and when the basket says pick with salmon (words to that effect) pick it up and you've tamed a salmon! Thank you 😘