Set the Instant Pot to sauté. Melt the butter, add the onion and celery, and cook 3 to 4 minutes. Add the garlic and cook 30 seconds more.
Add the cauliflower florets, stock, and bay leaf. Stir to combine.
Secure the lid, set the valve to sealing, and cook on high pressure for 8 minutes.
Let the pressure release naturally for 10 minutes, then quick-release any remaining pressure. Remove the bay leaf.
Using an immersion blender, puree the soup directly in the pot until smooth.
Stir in the heavy cream. Set the Instant Pot back to sauté on low.
Season the catfish with paprika, hot sauce, salt, and pepper. Add to the soup and simmer 5 minutes, until just cooked through.
Taste and adjust seasoning, then ladle into bowls and top with fresh chives.