Oh, that's interesting! I didn't know that. I knew about April Fools Day, even though it's not customary here, but had no idea about the relationship with fish
We do have a day that we observe, although it was more common in the time of my grandparents and today, most people don't identify it, but it's a similar idea to that of April Fools Day. I know it's known in other countries and it's the 28th of December, known as the Day of Innocent Saints or simply the Day of the Innocent. Jokes normally are on the same lines as for 1st April and once revealed, the joker wishes the victim well by telling them "¡Que la inocencia te valga!" ("May your innocence be worthwhile to you!").
