4 boneless white-fleshed fish fillets, 6 to 8 ounces each (such as whitefish or tilapia)
3 fresh juice tablespoons from about 3 limes, plus more to taste
4 1/2 tablespoons canola oil, divided
3 cups fresh corn kernels, from about 4 ears corn
3 cups Sun Gold tomatoes, quartered
1 to 2 jalapeños, stemmed, seeded, chopped (about 3 tablespoons)
1/2 large white onion, chopped (about 3/4 cup)
2 medium garlic cloves, minced (about 2 teaspoons)
Handful fresh cilantro, chopped
1/2 cup flour
3 tablespoons butter
Place fish fillets on a rimmed baking sheet and sprinkle with 2 tablespoons of lime juice and a couple pinches of salt. Set aside for at least 30 minutes.
Heat 1 1/2 tablespoons of canola oil in a 12-inch non-stick skillet over high heat until shimmering. Add corn kernels, toss well with a wooden spoon, and then spread evenly out. Cook until starting to char on the bottom, about 2 minutes. Stir well, and cook until corn starts to char again, another 2 minutes. Continue process until corn is evenly charred on all sides but not burnt, 8 to 10 minutes total. Transfer corn to a large bowl. Add the tomatoes, jalapeños, onion, garlic, cilantro, and remaining 1 tablespoon lime juice. Season with salt to taste. Add additional lime juice as necessary. Set aside.
Dry fish fillets on paper towels. Use a fork to mix together flour and a 3/4 teaspoon kosher salt in a large baking dish. Wipe out skillet and return to medium heat. Add butter and heat until melted. Dredge two fish fillets in the flour, shake off the excess, and then carefully place them in the skillet skin-side down. Cook until golden brown on the bottom, 3 to 4 minutes. Flip and brown on the other side, another 3 to 4 minutes. When both sides are browned and fish is cooked through, drain the fillets on a paper towel-lined plate and keep warm. Repeat process with the remaining 2 fillets.
Serve the fried fish with the corn salsa.