It is difficult to make out the details of that fish bones logo. But it looked somewhat familiar.
This is a picture of my "Blue Planet Surf Gear" rash guard I picked up at a thrift store several years ago.
Blue Planet Surf Gear rashguard, dark green, front-right by
C J, on Flickr
The logo is similar, but different. And in looking at the website for Blue Planet Surf Gear, the logo has been altered a little from the one on my gear, but it is still different from the logo on those swim briefs, as you can see, below.
Besides, as their name implies, Blue Planet makes
surf gear, and while rashguards are snug like swim briefs, they do serve a specific purpose for surfers to protect them from rashes (hence the name) -- but I am doubtful that
swim briefs have ever been a product they sell.
Guess we will have to keep looking for this mystery brand.