You have to plan this a week in advance to the week you want to win. Here’s what you do:
1. Fish up 38 Tastyfish during the contest.
2. Split them up into 2 stacks of 19.
3. Delete them.
4. Ticket a GM, and say you accidentally deleted them and wanted to turn them in for gold.
5. DO NOT retrieve them yet.
6. The next week, fish up 2 tastyfish, and seperate them into 2 stacks of 1.
7. Take the 2 stacks out of the mailbox. They will merge with your current stacks. (If you did not do step 6, they will simply disappear from the duration timer.)
8. Hand them in, enjoy the achievement and reward!