Below are two screenshots of the two bosses I have caught at Oxlease. I have spent 39 hours on this venue to catch the two fish but the game has not given me credit for the Ghost carp boss and I am a bit annoyed that Oxlease Mastery is still showing as incomplete. Not to mention, I didn't even get credit for it in Tier 1 Ultimate
I had an issue with my catches being reported for a day of so after the last dove tail live update. What fixed it for me was going into your in game options and signing out of DTL then restart the game and sign back in. I'm now only a few bosses away from completing all of the tier one Mastery challenges.
