How do you get a tentacool in FireRed?

In Pokémon FireRed, you can catch Tentacool by fishing or Surfing in the water. It is commonly found in the waters around Route 19, Route 20, and the Seafoam Islands. Use a Super Rod or Good Rod for a better chance, as Tentacool is more frequently encountered in these locations. Be prepared for battles, as it is a Water/Poison-type Pokémon.