Maer Dualdon FishermanG 10

You need a fishing rod to complete this and there are only two ways. First is if you got one during the Winter Event they have every year, which if it's not that event you are SoL. Assuming you don't have one, there is a daily quest to feed Lonelywood you will get every few days.

The trick here is you cannot catch 200lbs worth of fish (the quest objective) or the rod disappears and you will have to wait several more days to get another. Some fish weigh as much as 50lbs so do not let it go over 150lbs before you go and discard what you have already caught from your inventory. That will reset your quest progress back to 0/200 and you can keep fishing.

The achievement is for catching 200 fish NOT 200 lbs (like the quest). You can track this in your journal, I believe under General tab.