Most seafood is extremely low in carbohydrates, but it’s not all zero. Plain fish like salmon, tuna, and cod contain essentially no carbs. Shellfish, on the other hand, can carry anywhere from 2 to 7 grams per serving depending on the type. And processed seafood products like imitation crab can pack a surprising amount of starch and sugar.
Fish Is Practically Zero Carb
If you’re eating fin fish, you don’t need to think about carbs at all. Salmon, tuna, tilapia, cod, halibut, mahi-mahi, and virtually every other fish contain negligible carbohydrates per serving. The FDA groups seafood as providing negligible amounts of sugars and dietary fiber, and for plain fish that extends to total carbs as well. A 100-gram portion of cooked salmon or tuna registers at 0 grams of carbohydrate in standard nutrition databases.
This holds true regardless of preparation, as long as you aren’t adding breading, batter, or sugary glazes. Grilled, baked, broiled, poached, or pan-seared fish stays at zero carbs. The moment you coat it in flour or panko, the carbs come from the coating, not the fish itself.
Shellfish Carry a Few Grams
Shellfish are where the carb counts start to climb, though they’re still modest by any standard. The reason is a molecule called glycogen, which is the animal equivalent of starch. Bivalves like oysters, mussels, clams, and scallops store glycogen in their tissue as an energy reserve, and you eat the whole animal, glycogen included.
Scallops are one of the higher-carb shellfish. A 100-gram serving of steamed scallops contains about 6.3 grams of carbohydrates, with zero grams of sugar. Oysters typically fall in the 3 to 5 gram range per serving. Clams and mussels land in a similar neighborhood. The exact glycogen content in bivalves actually shifts with the seasons: oysters harvested in summer store significantly more glycogen than winter oysters, which is part of why summer oysters tend to taste sweeter and plumper.
Shrimp sits at the lower end, around 1 gram of carbohydrate per 100-gram serving, making it one of the leanest shellfish options if you’re counting carefully.
Squid and Octopus Fall in Between
Cephalopods, the category that includes squid (calamari) and octopus, contain a small but measurable amount of carbohydrate. A 3-ounce serving of cooked octopus has about 4 grams of carbs. Squid is similar, landing in the 3 to 4 gram range per comparable serving. Like bivalves, these animals store glycogen in their muscle tissue.
The catch with calamari is that it’s rarely served plain. Fried calamari rings can easily contain 15 to 25 grams of carbs per serving once you account for the batter and any dipping sauce. If you’re tracking carbs, the squid itself isn’t the problem. The breading is.
Imitation Crab Is a Carb Outlier
Imitation crab, also called surimi, is the one “seafood” product that genuinely adds up. It’s made from white fish paste mixed with starch, sugar, and other binders to mimic the texture and flavor of crab. A typical serving contains about 13 grams of total carbohydrate, including over 5 grams of sugar. That’s comparable to a slice of bread.
Surimi shows up in California rolls, crab rangoon, seafood salads, and pre-made sushi from grocery stores. If you’re eating what looks like crab in a budget-friendly context, there’s a good chance it’s surimi. Check the ingredient list for starches like tapioca or potato starch and added sugars. Real crab meat, by contrast, has less than 1 gram of carbohydrate per serving.
Seaweed Is Carb-Dense by Weight
Seaweed doesn’t fit neatly into the “seafood” category, but it shows up often enough alongside fish that it’s worth addressing. By dry weight, most edible seaweeds are 60 to 70% carbohydrate. However, much of that is fiber your body can’t digest. Some varieties like nori (the sheets wrapped around sushi) and certain brown seaweeds are almost entirely fiber, leaving very few digestible carbs. Others, particularly some green and red seaweeds, have higher net carb counts.
In practice, the amounts of seaweed most people eat are small enough that carbs stay low. A single nori sheet weighs about 2.5 grams, so even at high carbohydrate percentages, you’re looking at fractions of a gram per sheet. Seaweed salads served at restaurants use larger quantities and often include a sweetened dressing, which adds more carbs than the seaweed itself.
Quick Comparison by Type
- Fin fish (salmon, tuna, cod, tilapia): 0 grams of carbs per serving
- Shrimp: roughly 1 gram per 100g
- Squid and octopus: 3 to 4 grams per serving
- Clams, mussels, oysters: 3 to 5 grams per serving
- Scallops: about 6 grams per 100g
- Imitation crab (surimi): about 13 grams per serving
For anyone following a low-carb or ketogenic diet, plain fish is as close to zero carb as animal protein gets. Shellfish fit comfortably within most low-carb frameworks, though the few grams in scallops or oysters are worth tracking if your daily target is very strict. The real carb traps in seafood aren’t the seafood itself. They’re the breading, sauces, surimi fillers, and sweetened marinades that come along for the ride.