Basculin is not necessarily one of the Pokémon that you think about first when you think of the Pokémon series, but it has been around since the fifth generation of games and is at least a unique fish Pokémon to add to the ranks. While it does not retain its evolution from Pokémon Legends: Arceus in Pokémon Scarlet and Violet, you will need to catch one to complete your Pokédex. Here is where you can find and catch Basculin in Pokémon Scarlet and Violet.
How to catch Basculin in Pokémon Scarlet in Violet
Catching Basculin in Pokémon Scarlet and Violet is pretty simple. You just need to look for mostly any fresh water source. Outside of Casseroya Lake and the river that runs around Mesagoza, you should find groups of Basculin swimming around. They do not appear in salt water, so avoid the seas surrounding Paldea when looking for this Pokémon.
When you encounter a Basculin, it will likely try to initiate a battle with you, as they are aggressive creatures. It is only a Water-type, so it is weak against Electric and Grass attacks. We recommend not hitting it with these, as you might make it faint and lose out on the chance to catch it. That being said, we almost always saw Basculin swim together as a group, so you should have multiple chances to catch one.
While Basculin can potentially come with a red or blue mark down its body, the white mark version that was available in Pokémon Legends: Arceus is not in Scarlet and Violet. With that white mark form being the one that could exclusively evolve into Basculegion, there is no evolution for Basculin in Pokémon Scarlet and Violet, so you might look to just let your Basculin stay in a Box instead of battling with it.