Marlin vs Swordfish: How to Tell Them Apart (and Which You Can Eat)

Marlin vs swordfish comes down to two different families. Swordfish (Xiphias gladius, family Xiphiidae) has a long, flat, sword-shaped bill, no scales and no pelvic fins as an adult. Marlin (family Istiophoridae) has a rounder, spear-like bill, scales, pelvic fins and a taller, spikier first dorsal fin. Only one of them is a legal market fish on the US East Coast: swordfish.

If you are deciding what to eat, Florida has decided for you. Swordfish is a major commercial species sold as steaks; Atlantic marlin cannot be sold, so any marlin on an American plate was caught by the person eating it or landed in Hawaii.

Marlin vs swordfish at a glance

	Swordfish	Marlin (blue and white)
Family	Xiphiidae, the only species in it (Florida Museum)	Istiophoridae, with sailfish and spearfish
Bill	Long, flattened oval in cross section, a true “sword”	Round in cross section, shorter and spear-like
Scales and teeth	Adults lose scales by about 3 ft and have no jaw teeth	Scaled, with a fine lateral-line network on blue marlin
First dorsal fin	Tall, rigid, crescent-shaped; no pelvic fins	High at the front, slopes back; pelvic fins present
Max size	NOAA: about 1,165 lb; Florida Museum: up to 1,400 lb and 177 in	Blue marlin to about 14 ft and up to 2,000 lb; white marlin to 9 ft and 180 lb
Depth	Mainly 650–1,970 ft, dives past 2,100 ft; tolerates 41–80°F	Warm surface water above the thermocline, surface to about 330 ft
Sold as food in the US?	Yes, a managed commercial fishery	Not from the Atlantic; sale allowed only for Hawaii and Pacific Insular Area landings
Flavor (NOAA)	Slightly sweet, moist, firm, moderate oil	Rich, full flavor; firm and meaty, “similar to swordfish”
Nutrition	Cooked, per 100 g (USDA): 172 kcal, 23.4 g protein, 7.9 g fat, about 0.9 g EPA+DHA	Per 4 oz (NOAA): 120 kcal, 29 g protein, 0.5 g fat; no USDA entry
FDA mercury category	Choices to Avoid	Choices to Avoid

Is swordfish and marlin the same fish?

No. Both are “billfish” in everyday speech, but swordfish sits alone in Xiphiidae while every marlin, sailfish and spearfish belongs to Istiophoridae. The Florida Museum lists three features that separate swordfish from the rest: bill shape, no teeth in adults, and no pelvic fins.

From a boat the confusion is understandable: both are big, dark-backed predators with a crescent tail that slash through bait with the bill. Up close, the differences are obvious.

Marlin vs swordfish bill: flat sword or round spear?

The bill is the fastest tell. The Florida Museum describes the swordfish bill as “a flattened oval in cross section” and long relative to other billfish; the Latin gladius means sword. A blue marlin’s bill is round in cross section and proportionally shorter, closer to a spear than a blade. The white marlin profile uses the same description: round, long and slender.

Fin shape confirms it. A swordfish’s first dorsal fin is tall, rigid and sickle-shaped, with no pelvic fins beneath. Blue marlin have a high dorsal fin that slopes steeply backward plus visible pelvic fins; white marlin have a rounded front tip on the dorsal fin, which is how anglers separate them from blues.

Marlin vs swordfish size: which gets bigger?

Blue marlin win on paper. The Florida Museum says blue marlin grow to 14 feet and “up to a ton,” and NOAA’s Pacific blue marlin profile puts the ceiling past 12 feet and 2,000 pounds, with females far larger than males. Swordfish top out lower: NOAA lists a maximum of about 1,165 pounds, the Florida Museum cites 1,400 pounds and 177 inches, and the rod-and-reel record it reports is 1,182 pounds.

Most fish are nowhere near those numbers. NOAA says swordfish are “usually 50 to 200 pounds” when caught, and white marlin, the smaller Atlantic species, max out around 9 feet and 180 pounds.

Where do marlin and swordfish live off Florida?

Both roam the Gulf Stream at different depths. NOAA calls the Gulf and Florida Straits important swordfish nursery grounds, and the Florida Museum places adults mostly at 650–1,970 feet, diving past 2,100 feet, which is why Florida swordfish trips run at night or deep-drop by day. Marlin stay up top: NOAA says blue marlin prefer warm, wind-mixed surface water and spend most of their time between the surface and 100 meters.

Both are sportfishing royalty: NOAA dates recreational swordfishing off the East Coast to the 1920s, and marlin headline every offshore tournament. Atlantic marlin are recreational-only, with NOAA minimum sizes of 99 inches for blue and 66 inches for white marlin (lower jaw to tail fork) and US landings of blue marlin, white marlin and roundscale spearfish capped at 250 a year.

Can you eat marlin?

You can, but you probably will not buy it in Florida. NOAA’s Billfish Conservation Act page states that Atlantic billfish sales have been banned by regulation since 1988, and the 2012 Act made it illegal nationwide to sell or possess for sale black marlin, blue marlin, white marlin, striped marlin, sailfish and spearfish. Swordfish is explicitly exempt from the Act’s definition of billfish.

The exception is the Pacific. Billfish landed in Hawaii or the Pacific Insular Areas may be sold, and NOAA reports 1.3 million pounds of blue marlin landed commercially around Hawaii in 2024, sold as kajiki or a’u. The Florida Museum calls blue marlin “a popular sushi fish in Japan” and common table fare in Hawaii; the Hawaii Seafood Council lists it for poke, sashimi, grilling and smoking.

What does marlin taste like compared to swordfish?

Marlin is the bolder of the two. NOAA describes Pacific blue marlin as “rich, full flavor” with flesh that is “firm and meaty, similar to swordfish,” light golden-orange when raw and off-white when cooked. The Hawaii Seafood Council rates the flavor mild to pronounced and the texture firm, and notes high-fat fish are preferred raw.

Swordfish is milder and more forgiving. NOAA calls it “moist and flavorful with a slightly sweet taste,” firm, with moderate oil; our swordfish taste guide covers it in detail. In the kitchen, marlin behaves like a leaner, stronger swordfish: NOAA’s label shows 0.5 g of fat per 4-ounce serving against 7.9 g per 100 g for cooked swordfish, so marlin dries out faster on a grill and shines raw or smoked.

Both carry the same warning. The FDA/EPA fish advice puts marlin and swordfish on its “Choices to Avoid” list for pregnancy, breastfeeding and children ages 1–11, alongside shark, king mackerel and bigeye tuna. Other adults should treat both as occasional fish, not a weekly staple.

Swordfish vs marlin vs sailfish

	Swordfish	Blue marlin	Sailfish
Family	Xiphiidae	Istiophoridae	Istiophoridae
Bill	Flat, long sword	Round spear	Round, slender
Signature fin	Tall, rigid sickle	High, steeply sloped	Sail taller than the body
Max size	About 1,165–1,400 lb	Up to 2,000 lb	Atlantic fish about 128 lb; Florida fish 68–90 in
Where off Florida	Deep, 650–2,100 ft	Warm surface water	Nearshore to offshore surface water
Sold as food in the US	Yes	Hawaii landings only	No; “rarely sold unless smoked” (Florida Museum)
Eating quality	Mild, steaky	Rich, firm, best raw or smoked	Tough, usually released

Our sailfish vs swordfish guide covers Florida’s state saltwater fish in detail, including the speed claims.

Which should you order?

Order swordfish when you want a thick, mild steak that holds together on a grill; plain grilled or blackened shows it best. If you want something firmer and richer, yellowfin or bluefin tuna is the closest legal stand-in for marlin on an East Coast menu; our tuna taste guide explains how it eats.

For a lighter alternative with the same grill-friendly firmness and none of the mercury warning, mahi mahi and wahoo are the Florida standbys; Fish On Fire’s menu runs mahi grilled, blackened or fried. If you are offered marlin in Hawaii, order it as poke or smoked, where its fat and flavor do the work.

Bottom line

Swordfish and marlin are different families you can tell apart by the bill: flat sword versus round spear, plus scales and pelvic fins on marlin and none on swordfish. Blue marlin grow bigger, swordfish live deeper, and only swordfish is sold from Atlantic waters. Both land on the FDA’s highest-mercury list, so enjoy either in moderation.

Marlin vs Swordfish: What's the Difference?