Nearly all seafood contains some iodine, but the amounts vary dramatically. A single serving of cod or haddock can deliver your entire daily iodine needs, while the same portion of tilapia or catfish barely registers. The recommended daily intake for adults is 150 mcg, rising to 220 mcg during pregnancy and 290 mcg while breastfeeding. Knowing which seafood delivers the most iodine helps you hit those targets without overthinking it.
White Fish: The Standout Source
Cold-water white fish are the most reliable seafood source of iodine, and two species dominate the list. Haddock contains roughly 250 mcg per 4-ounce raw serving, enough to exceed an adult’s entire daily requirement in one meal. Baked cod comes in close behind at 146 mcg per 3-ounce cooked serving. Alaska pollock, the fish most commonly used in fish sticks and fast-food sandwiches, provides about 48 mcg per 4-ounce serving.
After those top three, iodine levels drop off sharply. Flounder and sole deliver around 16 mcg per serving. Rockfish and ocean perch sit in a similar range at 12 to 15 mcg. And some of the most popular everyday fish are near the bottom: tilapia provides just 5.8 mcg per serving, swai about 8.5 mcg, and catfish a mere 2.7 mcg. If you’re eating fish specifically for iodine, the species you choose matters far more than simply “eating more fish.”
Why Iodine Content Varies So Much
The ocean itself is rich in iodine, but fish absorb it at different rates depending on their diet, habitat, and physiology. Cold-water bottom dwellers like cod and haddock feed on iodine-rich organisms along the sea floor, which concentrates the mineral in their flesh. Tropical freshwater species like tilapia and catfish live in environments with far less iodine available.
Whether your fish is farmed or wild-caught also plays a role. Research on Atlantic halibut found that farmed fish contained less iodine than wild-caught halibut, likely because commercial fish feed delivers less iodine (or less bioavailable iodine) than a natural ocean diet. This pattern likely extends to other farmed species, though the gap varies.
Seaweed: Extremely High but Hard to Predict
Seaweed is technically the most iodine-dense seafood on the planet, but the concentrations are so variable that it’s difficult to use as a precise dietary source. Brown seaweeds contain far more iodine than red varieties. Dried kombu (kelp) tops the chart at 2,100 to 4,300 mg per kilogram, meaning even a small piece could contain hundreds or thousands of micrograms of iodine. That’s well beyond daily needs and potentially above safe limits.
Other brown seaweeds fall across a wide spectrum. Hijiki contains around 790 mg/kg dried, wakame ranges from 220 to 280 mg/kg, and arame sits around 540 mg/kg. Nori, the thin sheets used to wrap sushi, is the lowest at just 9 to 20 mg/kg dried, making it the safest seaweed to eat regularly without worrying about excess iodine. A single nori sheet weighs about 2.5 grams, so even at the higher concentration you’re only getting around 50 mcg per sheet.
The practical takeaway: nori is a reasonable, low-risk iodine source you can eat frequently. Kombu and other thick kelp products should be used sparingly, more as a flavoring agent in broths than eaten in large quantities.
How Much Iodine Is Too Much
The tolerable upper intake level for adults is 1,100 mcg per day. Going above that consistently can disrupt thyroid function, potentially causing either an overactive or underactive thyroid. Most fish-based meals won’t get you anywhere near that ceiling. Even a generous serving of haddock keeps you well under 300 mcg. The real risk comes from seaweed, particularly kombu, where a few grams of dried product could push you past the upper limit in a single sitting.
Cooking Affects How Much Iodine You Actually Get
The way you prepare fish changes its final iodine content. Boiling causes the largest loss, stripping away about 37% of the iodine as it leaches into the cooking water (unless you drink the broth). Shallow frying loses around 27%, deep frying about 20%, and steaming roughly 20%. Roasting or baking preserves the most iodine, with only about 6% lost during cooking. If maximizing iodine is your goal, baking or roasting your fish is the best approach.
Quick Comparison by Serving
- Haddock (4 oz raw): 250 mcg
- Cod, baked (3 oz): 146 mcg
- Fish sticks, frozen (3 oz): 57 mcg
- Alaska pollock (4 oz raw): 48 mcg
- Flounder/sole (4 oz raw): 16 mcg
- Rockfish (4 oz raw): 15 mcg
- Ocean perch (4 oz raw): 12 mcg
- Halibut (4 oz raw): 11 mcg
- Swai, cooked (3 oz): 8.5 mcg
- Tilapia, baked (3 oz): 5.8 mcg
- Catfish, pan-cooked (3 oz): 2.7 mcg
Putting It Together
If you’re looking to boost your iodine intake through seafood, cod and haddock are the most efficient choices by a wide margin. A single serving of either one covers your daily needs. Pollock is a solid mid-range option, especially in affordable forms like frozen fish sticks. For non-fish options, nori sheets offer a modest and safe iodine boost, while kombu should be treated more like a seasoning than a food.
Popular fish like tilapia, catfish, and swai are fine protein sources, but they contribute almost no meaningful iodine. If those are your go-to fish and you’re concerned about iodine, you’ll need to get it elsewhere, whether from other seafood, iodized salt, or dairy products.