Hmm. I'm very surprised someone managed to catch death fish before level 6. I was under the impression that you needed to be level 7.
But to catch without bait you do need to be level 10 (9 if angler).
To catch with bait (angelfish) you need to be level 7 (6, possibly 5 if angler)
And with bait and a level 10 fisherwoman, I've managed 7 regularly. I also didn't have that one skill challenge done yet, so that might make it faster.