Wild Bait is a type of bait that makes it possible to catch two fish at the same time and also makes fish bite slightly faster than standard bait. Wild Bait can be crafted after being taught the recipe by Linus during his 4-heart cutscene. Once the recipe is known it is also possible to obtain Wild Bait from Fishing Treasure Chests. It is possible to find Wild Bait in artifact spots on Ginger Island even before triggering the cutscene with Linus.
Wild Bait cannot be used with the Training Rod or the Bamboo Pole. Only the Fiberglass Rod (unlocked at Fishing level 2) or the Iridium Rod (unlocked at Fishing level 6) can use bait. Wild bait can also technically be used in a Crab Pot, but it is no better than standard bait: crab pots never produce double fish.