Make the crawfish sauce: In a saucepot, heat oil over medium-high. Add onion, celery, pepper, and garlic and sauté until translucent. Add Cajun spice and stir for 1 minute until vegetables are completely coated. Add tomato paste and cook for 3 to 4 minutes until paste is slightly toasted. Add seafood stock and heat until simmering. Whisk in dark roux and reduce heat to low. Simmer for 15 minutes. Add tomatoes and crawfish tails and season with salt and Tabasco. Make the catfish: Season each piece of fish with 1 tablespoon Cajun spice. In a large sauté pan set over high heat, add oil and heat until shimmering. Add catfish and reduce heat to medium-high; sauté until a crust forms on the fish, about 2 minutes per side. Add crawfish sauce to pan and simmer over low heat for 2 minutes until catfish is tender and almost falls apart. Serve catfish and sauce over cooked rice.