Chilean Sea Bass Soup with Potatoes and Fennel

Chilean sea bass soup is a generous, tomato-based seafood soup with tender potatoes, aromatic fennel, and buttery pieces of fish. This home-style version is inspired by coastal cooking rather than presented as a single traditional Chilean recipe; its mild broth lets the rich, flaky fish shine.

Ingredients

1½ lb Chilean sea bass fillets (680 g), skin removed and pin bones checked
1 tbsp olive oil (15 ml)
1 medium yellow onion (about 150 g), finely chopped
1 small fennel bulb (about 250 g), trimmed, cored, and diced; reserve a little frond for garnish if available
2 celery stalks (about 80 g), diced
3 garlic cloves (about 9 g), minced
1 tbsp tomato paste (16 g)
½ tsp smoked paprika (about 1 g)
½ cup dry white wine (120 ml), or use an additional ½ cup (120 ml) fish or chicken stock
5 cups fish stock (1.2 L), preferably low-sodium; chicken stock works in a pinch
1 lb waxy potatoes (450 g), such as Yukon Gold, cut into ½-inch (1.25 cm) cubes
1 can crushed tomatoes, 14.5 oz (411 g)
1 bay leaf (about 0.2 g)
1 tsp fine salt (5 g), plus more to taste
¼ tsp freshly ground black pepper (about 0.5 g), plus more to taste
1 tbsp fresh thyme leaves (about 3 g), or 1 tsp dried thyme (about 1 g)
2 tbsp chopped fresh parsley (about 8 g)
1 tbsp fresh lemon juice (15 ml), plus lemon wedges for serving

Instructions

Prepare the ingredients. Pat the fish dry and cut it into roughly 1½-inch (4 cm) chunks, checking for any remaining pin bones. Chop the onion, fennel, celery, garlic, and potatoes as directed. Keep the fish refrigerated while you start the soup, and set out the measured seasonings and liquids so they are ready to add.
Soften the vegetables. Heat the olive oil in a large, heavy soup pot or Dutch oven over medium heat. Add the onion, fennel, and celery with a small pinch of the measured salt. Cook for 6 minutes, stirring from time to time, until the vegetables have softened and the onion looks translucent. If the bottom begins to brown before the vegetables soften, lower the heat rather than adding extra oil.
Build the tomato base. Stir in the garlic, tomato paste, and smoked paprika. Cook for 2 minutes, stirring constantly so the garlic does not scorch and the paste darkens slightly. Pour in the wine and simmer for 2 minutes, scraping up any flavorful bits from the bottom of the pot. If you are not using wine, add the same amount of stock at this point.
Simmer the potatoes. Add the fish stock, crushed tomatoes, potatoes, bay leaf, thyme, remaining salt, and black pepper. Bring the liquid to a gentle boil, then lower the heat to maintain a steady simmer. Cook uncovered for 12 minutes, stirring once or twice, until the potatoes are almost tender when pierced with a knife. They should not be falling apart; they will finish cooking with the fish.
Cook the fish gently. Lower the heat so the soup barely simmers. Add the fish chunks in a single layer as much as the pot allows, then gently stir once to submerge them. Cook for about 8 minutes, avoiding a hard boil that can break up the fish. Check the thickest piece with a food thermometer: the USDA FSIS safe minimum internal temperature for fish is 145°F (63°C). The flesh should also look opaque and separate into moist flakes. If a piece has not reached temperature, simmer a little longer and check again.
Finish and taste. Remove the bay leaf. Stir in the parsley and lemon juice carefully so the fish stays in generous pieces. Taste the broth and adjust the salt, pepper, or lemon as needed. Ladle into warm bowls, adding a little fennel frond or extra parsley if you have it, and serve right away.

Tips

Choose a close fish substitute if needed. Chilean sea bass is sold under that market name for Patagonian toothfish and may be costly or unavailable. Halibut is a good substitute for a firm, substantial bite; cod is milder and flakes more readily, so add it gently and avoid stirring once it is in the pot. Either substitute should reach 145°F (63°C).
Keep the simmer gentle. A rolling boil can make delicate fish break into small flakes and may cause the potatoes to crumble. Once the fish goes in, reduce the heat and let the broth move softly around it. If the soup stops simmering after you add cold fish, give it a moment to return to a gentle simmer before starting the doneness check.
Cut the potatoes evenly. Pieces close to ½ inch (1.25 cm) cook at a similar pace. Large chunks may still be firm when the fish is ready; very small dice can turn mushy. Waxy potatoes hold their shape better than floury varieties, although russets can be used if you prefer a thicker, softer broth.
Season in stages. Stock and canned tomatoes vary in saltiness, so the measured salt is a starting point, not a reason to skip tasting. Add most of it with the broth, then adjust after the fish is cooked. Lemon brightens the soup, but add it gradually so it complements rather than overwhelms the tomato and seafood.

Serving Suggestions

Serve the soup hot in wide bowls so every portion gets fish, potatoes, and plenty of broth. Crusty bread, toasted sourdough, or warm rolls are useful for soaking up the tomato broth. For a lighter side, offer a simple green salad with a sharp vinaigrette; its crispness balances the rich texture of the sea bass without competing with the soup.

Set lemon wedges, chopped parsley, and a small bowl of extra black pepper on the table so diners can finish their own bowls. If you want a more substantial meal, serve the soup with a small plate of roasted vegetables or a scoop of plain rice. Keep those accompaniments simply seasoned, since the broth already has tomato, herbs, and aromatic vegetables.

Variations

Make it without wine: Replace the wine with an equal amount of stock, as listed. Wine gives the broth a little acidity and depth; stock makes the flavor rounder and slightly less sharp. A few extra drops of lemon at the end can restore some brightness if you miss that contrast.

Use another firm fish: Halibut, cod, haddock, or pollock can replace the sea bass. Firm halibut stays in large pieces, while cod and pollock are more likely to flake into the broth. Add similarly sized pieces and use a thermometer rather than relying only on the clock, because thickness and fish type change cooking time.

Add shellfish: Small peeled shrimp can be added during the final few minutes, but they cook quickly and should not be left simmering while the fish finishes. Mussels are another option if they are fresh and handled safely; add them earlier than the fish and cook until their shells open, discarding any that remain closed. Avoid crowding the pot, which can slow heating and make timing less predictable.

Change the vegetable profile: Replace the fennel with an extra celery stalk and a small sliced leek if fennel is hard to find. The soup will lose fennel’s gentle anise-like aroma and taste more savory and onion-forward. A pinch of red pepper flakes can add warmth, while a little extra thyme keeps the broth herbaceous without changing its basic character.

Storage and Reheating

Refrigerate leftover soup within 2 hours of cooking, transferring it to shallow airtight containers so it cools promptly. Keep it refrigerated for 3–4 days. Fish continues to absorb broth as it sits, and its texture becomes more delicate, so the soup is usually at its best the day it is made or the next day.

For the best texture, reheat only the portion you plan to eat. Warm it slowly in a covered saucepan over low to medium-low heat, stirring carefully and stopping when it is steaming throughout. Leftovers must reach 165°F (74°C) when checked with a food thermometer. Avoid bringing the soup to a prolonged boil, which can break up the fish and soften the potatoes further. A microwave also works: use a covered microwave-safe bowl, heat in short intervals, and stir gently between intervals to distribute the heat.

Freezing is possible, but the fish and potatoes may become softer after thawing. If freezing, cool the soup promptly, pack it in freezer-safe containers with room for expansion, and freeze for up to 2 months for best quality. Thaw it overnight in the refrigerator and reheat to 165°F (74°C). Do not leave the soup at room temperature to cool for an extended period, and do not try to preserve it in a jar or at room temperature.

Frequently Asked Questions

Is Chilean sea bass the same fish as Patagonian toothfish?
Chilean sea bass is the common market name for Patagonian toothfish. The fish is not necessarily caught off Chile, so the name does not describe the origin of every fillet. Check the package or ask the fish seller about its source and handling.

Can I use frozen Chilean sea bass?
Yes. Thaw it in the refrigerator, not on the counter, then pat it dry and cut it into chunks. If the fish releases a lot of liquid during thawing, drying it well helps keep extra water from diluting the broth. Keep it chilled until you are ready to add it to the pot.

How can I tell when the fish is done?
Check the thickest piece with a food thermometer; it should reach 145°F (63°C). The flesh should be opaque and flake easily, but visual cues alone are less dependable than checking the temperature. Insert the thermometer from the side into a large chunk for a useful reading.

Can I prepare the soup ahead of time?
You can make the tomato, vegetable, and potato broth a day ahead, cool it promptly, and refrigerate it. Reheat the broth until simmering, then add the fish and cook it just before serving. This keeps the fish from becoming overcooked during storage and reheating.

Why is my soup too thin or too thick?
The broth is meant to be spoonable rather than creamy. For a thinner soup, stir in a little warm stock. For a thicker result, mash a few cooked potato pieces against the side of the pot and stir them back in. Avoid blending the whole soup, which would break up the fish and change its texture.

Can I make it without fennel?
Yes. Use leek, extra celery, or a little more onion instead. Fennel gives the soup a mild, distinctive aromatic note; leaving it out makes the flavor more familiar and savory, but the tomato, thyme, and fish still make a balanced bowl.

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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

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