What does it mean when it says swarm above pokemon location?

Question

It says it for qwilfish and remoraid

Answer 1

It means that the Pokemon only appears during a swarm. A swarm is when a specific pokemon appears in one area for a short time. It's available after you complete the game, similar to Diamond/Pearl.

I don't know exactly how the game tells you but it's likely on the TV or one of the characters in game will tell you where the swarms are.

Comments

The swarms will be posted in the little rooms when moving from one city to another (the word that pass by the monitor)