In large dutch oven add 4 tablespoons butter on medium-high heat and let melt. Add onion. Stir continuously for 2-4 minutes or until onions start to cook down. Push onions to the sides of the pan and add garlic in the middle. Add olive oil on top of garlic and let it cook until it becomes fragrant. Then mix garlic and onion together and continue to let it cook down for another minute.

Add celery, a sprinkling of black pepper, 1/8 teaspoon salt, and let that cook down with the garlic and onion, still stirring, for another 2-4 minutes.

Add seafood stock, tomatoes, coconut milk, paprika, red pepper flakes, and 1 teaspoon salt. Stir to combine.

Take shrimp shells and place in cheesecloth. Bring corners up and use kitchen twine to tie the pouch around the shells. Place in the broth and let simmer 1 hour.

While that simmers, bring a cast iron skillet to medium-high heat and cut the sea bass (or swordfish) into large chunks - season with a little salt and pepper. Add 1 tablespoon butter to the skillet and sear fish approx. 1 minute on all sides (no need to cook it all the way through) - complete in batches, if needed. Remove from skillet and transfer to a plate and set aside.

Remove pouch of shrimp shells from the soup pot and discard.

Add cilantro, lime juice, and potatoes to the broth - let simmer approx. 8-10 minutes or until potatoes are firm, but soft.

Add seared fish and uncooked shrimp to the large pot. Cover and let simmer 5-10 minutes or until shrimp and fish are cooked through. 

Taste and add any additional salt, pepper, or lime juice, as desired.

Serve with rice, fresh cilantro, and lime wedges.