If you're a knowledge chaser, I'm here to let you know that for me this was the hardest fish knowlwegde to get. I say was but I don't have it yet. Caught it 7 times, still no knowledge. You have to count about 3-4 hours for every catch in average. PA needs to realise 30% knowledge drop chance on something that takes so long to catch is not ok. I feel you shouldn't have to grind more than 30 hours for a lifeskill related knowledge... I've been unlucky, sure, but not incredibly so either, I mean 70% fail chance is bad enough it could take you more than 10 tries, anyone who's enhanced long enough knows this. I'll update this post when I get it and let you know how many catches it took.

Edit: Took 9 catch in the end. So something like 40 hours of harpooning. May you be more lucky than I was if you're going for this knowledge...