Heat the oil in a large stockpot over medium heat. Add the onions and cook until softened, about 5 minutes. Add the garlic and cook, stirring, 1 more minute.
Stir in the salt, pepper, dried thyme, paprika, and cayenne.
Add the clam juice. Bring to a gentle simmer.
Add the fish pieces. Make sure they are completely submerged. If not, add a little water or more broth.
Bring the soup back to a gentle simmer. Reduce the heat to low and cover the pot. Cook on low simmer until the fish is just cooked through, 5-7 minutes.
Heat the heavy cream in the microwave for 60 seconds. Stir it into the soup. Turn the heat off.
Divide the chowder between four bowls. Top with parsley and bacon bits and serve.
As you can see, this chowder is very high in sodium. While this is typically not a concern on the keto diet, if this is a concern for you, you could omit the bacon and the salt. According to my estimate, this should reduce the sodium to 897 mg per serving. Since it's made without potatoes (and the starch they add), this chowder is not thick - it has the consistency of a rich soup. If you'd like to thicken it, you can use any keto thickener that you like. One example is glucomannan powder - try mixing ½ teaspoon in a tablespoon of cold water and stirring that into the finished soup. However, keep in mind that authentic chowders are not necessarily thick.