When you bond with Trout, you get trueswim. What is trueswim?

You'll automatically tread water, and swimming to/from a water room deals no damage. Additionally, you're able to breathe water.

Aha. Thanks!

The waterbreathing part isn't part of trueswim, though. Trueswim is a skill in...environment? Waterbreathe is one of my enchantments (Revan does it worse.)

Trueswim is not a skill an environment.

ab environment
You have gained the following abilities in Environment:
Fluidswim Swimming with not a care in the world.
AB ENVIRONMENT for more information on an ability.

Close enough.

Yes, that's the one I meant. Although the difference could account for the waterbreathing. Regardless, Trout = waterbreathe + fluidswim.