Attention all Fly Knights,

There are 10 fish that can be caught and eaten to gain temporary buffs. All of these fish can be found in the large underground pond. The pond can be accessed from the Tower of Anticipation bonfire. Take the lift down and you are there. Just catch all the fish.

But the 11th fish is actually a weapon. Once you release the floodgate at the end of the Ruins map, jump on to a boat and let it carry you to the next area. After you jump out of the boat on to the doorway, look to the end of the stream where all the boats go. At the very end of it, you can find a swordfish swimming around. Catch it like normal and you can then equip it as a sword. The achievement should also unlock, if it was the last fish you needed to catch.

That is all.