Bring a large heavy-duty pot of well-salted water to a boil. Meanwhile, tear the kale leaves from their ribs. Discard the ribs and tear the leaves into bite-size pieces. Wash well. Cook the greens in the boiling water until tender, about 5 minutes. Drain in a large-mesh sieve, pressing firmly on the greens with the back of a large spoon to extract as much liquid as possible.
Using the same pot, heat 1 Tbs. of the oil over medium heat. Add the shallot and garlic and cook, stirring constantly with a wooden spoon, until tender but not browned, about 2 minutes. Return the greens to the pot, add the crème fraîche, and toss with tongs to combine. Season totaste with salt and pepper; remove from the heat, cover, and keep warm.
In a small bowl, combine the paprika, celery salt, cayenne, and 1/4 tsp. each salt and pepper. In a heavy-duty 12-inch nonstick skillet, heat the remaining 2 Tbs. oil over medium-high heat. Brush the catfish with the lemon juice and sprinkle both sides evenly with the spice mixture. Put the fish in the pan, reduce the heat to medium, and cook until browned, 4 minutes. Carefully flip the fish with a spatula and cook until it flakes easily when tested with a fork, 3 to 4 minutes. Serve the fish over the greens.