Manhattan Cod Chowder

Heat oil in a large saucepan over medium-high heat. Add onion, celery, garlic, tomato paste and thyme and cook, stirring, until the vegetables are just starting to brown, 3 to 5 minutes. Add broth, water, tomatoes (with juice) and potatoes; bring to a simmer over high heat. Reduce heat to maintain a simmer and cook until the potatoes are tender, 10 to 12 minutes. Add cod and cook, gently stirring occasionally, until just cooked through, 4 to 5 minutes more. Season with pepper and salt.