Swordfish vs Sailfish for Kids
Swordfish and sailfish are both ocean-going billfishes, but they belong to different families and are easy to separate when the whole body is visible. The swordfish, Xiphias gladius, is the only living species in family Xiphiidae. The sailfish is treated here as Istiophorus platypterus, following evidence that Atlantic and Indo-Pacific populations do not require two separate species. A swordfish is far heavier, deeper-diving, and equipped with a flat broad bill; a sailfish is slimmer, scaled, and topped by an enormous flexible dorsal fin.
Swordfish
- Type: Fish
- Group: Species: Xiphias gladius; only living member of family Xiphiidae
- Known for: Large cylindrical body, long flat broad bill, tall curved first dorsal fin, no pelvic fins, crescent tail, scale-free toothless adults, deep dives, and a brain-and-eye heater
- Diet: Carnivore
- Special skill: Keeping the eyes and brain warmer than deep water while a flat powerful bill helps disable fish and squid
Sailfish
- Type: Fish
- Group: Species: Istiophorus platypterus; family Istiophoridae
- Known for: Slender compressed body, round spear-like bill, enormous spotted first dorsal sail, long pelvic fins, small scales and teeth, blue bars, agile turns, and group attacks on schooling fish
- Diet: Carnivore
- Special skill: Folding long fins into grooves for streamlined travel, then using a rapid narrow bill, body colour changes, and group alternation around fish schools
Quick Answer
Quick answer: A swordfish has a long flat broad bill, a heavy round body, a short-based high first dorsal fin, no pelvic fins, and no scales or jaw teeth as an adult. A sailfish has a rounder spear-like bill, a slimmer compressed body, a giant sail running along most of the back, long pelvic fins, small scales, and small teeth. Swordfish grow much heavier and dive deeper; sailfish are famous for colour changes and group hunting around schooling fish.
Swordfish vs Sailfish: Quick Comparison
| Feature | Swordfish | Sailfish |
|---|---|---|
| Scientific name | Xiphias gladius | Istiophorus platypterus |
| Family | Xiphiidae; only living species | Istiophoridae with marlins and spearfishes |
| Bill shape | Long, wide, and flattened like a broad blade | Long, slender, and nearly round like a spear |
| First dorsal fin | High, rigid-looking, and short-based in the adult | Very tall flexible sail running along most of the back |
| Pelvic fins | Absent | Very long and foldable into ventral grooves |
| Adult surface | No scales, jaw teeth, or visible lateral line | Small scales, small teeth, and a visible lateral line |
| Maximum mass | Several hundred kilograms; exceptionally over 500 kilograms | About 100 kilograms in the largest recorded examples |
| Typical depth use | Wide vertical range, including deep cold water beyond 600 metres | Mainly warm upper-ocean water, commonly above about 100 metres |
| Hunting pattern | Usually solitary opportunistic pursuit of fish and squid | Can alternate bill attacks with other sailfish around schooling prey |
| Standout adaptation | Eye-and-brain heater for rapid deep vertical movement | Huge sail, rapid colour change, and agile group-feeding manoeuvres |
How Are Swordfish and Sailfish Alike?
- Both are bony billfishes with an elongated upper jaw used while capturing fish and squid.
- Both have streamlined open-ocean bodies, powerful crescent-shaped tails, countershading, and keels near the tail base.
- Both live across warm parts of the Atlantic, Pacific, and Indian Oceans and make long pelagic movements.
- Both are carnivores that often target schooling fishes, cephalopods, and other fast marine prey.
- Both reproduce by releasing many small buoyant eggs, and their tiny larvae look very different from the adults.
How Are Swordfish and Sailfish Different?
- A swordfish belongs to family Xiphiidae, while a sailfish belongs to Istiophoridae with marlins and spearfishes.
- The swordfish bill is broad and flat in cross-section; the sailfish bill is slimmer and nearly round.
- An adult swordfish lacks scales, jaw teeth, pelvic fins, and a visible lateral line; an adult sailfish retains all four features.
- Swordfish become far heavier and regularly enter much deeper colder water, while sailfish are smaller upper-ocean specialists.
- The swordfish has a high short-based first dorsal fin; the sailfish has a giant flexible first dorsal sail extending along most of the back.
Swordfish vs Sailfish Showdown
Adaptation showdown: The swordfish wins size because the largest reliable adults are several times heavier than sailfish. Speed is a tie: both are fast, but popular maximum-speed figures come from incompatible observations and calculations rather than one controlled race. The swordfish takes strength for its much greater mass and broad robust bill. Stealth is a tie between deep-water countershading and the sailfish’s almost invisible slow bill insertion before a rapid swipe. The sailfish wins social behaviour because filmed groups alternate attacks and benefit from one another’s hunting actions. Swimming is a tie between swordfish depth-and-temperature endurance and sailfish upper-ocean manoeuvrability. The swordfish wins the weirdest-adaptation prize for converting part of an eye muscle into a heater that warms its brain and eyes.
Fun Swordfish vs Sailfish Facts
One Bill Is Flat and One Is Round
The swordfish’s upper jaw forms a long broad blade with a flattened oval cross-section. The sailfish’s bill is narrower and nearly circular. Both can make rapid sideways movements, so neither should be drawn using the bill like a permanently embedded spear.
Adult Swordfish Lose Scales and Teeth
Young swordfish pass through dramatic body changes. By adulthood, the skin lacks ordinary scales, the jaws lack teeth, pelvic fins are absent, and the lateral line is no longer visible, while adult sailfish keep small scales, small teeth, long pelvic fins, and a visible lateral line.
The Sail Changes with Excitement
A sailfish can vary its body colour and display pale blue bars and spots more strongly when excited. The huge first dorsal fin is flexible rather than a rigid wall and can be lowered for streamlined travel or raised during manoeuvres and display.
Sailfish Take Turns Around a School
Field observations show groups of sailfish alternating attacks on sardine schools. One individual’s bill action may injure prey that another later catches, producing cooperative benefits without every movement being tightly coordinated.
A Swordfish Heats Its Eyes and Brain
Part of an extraocular muscle is modified into heat-producing tissue supplied by a vascular heat exchanger. This cranial heater slows cooling of the eyes and brain while a swordfish moves rapidly through water layers with very different temperatures.
Swordfish vs Sailfish Quiz
- Which fish has a broad flattened bill? Answer: Swordfish.
- Which fish has a giant dorsal sail? Answer: Sailfish.
- Which adult lacks pelvic fins and ordinary scales? Answer: Swordfish.
- Which fish has been observed alternating attacks in groups? Answer: Sailfish.
- Why is the speed category a tie? Answer: Published and popular speed values were not measured under one comparable test.
Swordfish vs Sailfish FAQ
What is the easiest way to tell a swordfish from a sailfish?
Look at the first dorsal fin and bill. A swordfish has a high triangular adult fin and a flat broad bill. A sailfish has a huge sail extending along most of its back and a thinner round bill.
Which is bigger, a swordfish or a sailfish?
The swordfish is much heavier. Both can reach several metres including the bill, but a huge swordfish can weigh several hundred kilograms, while the largest sailfish records are around 100 kilograms.
Is the sailfish definitely the fastest fish?
No controlled test has compared maximum speed across all large fishes. Both species are fast, but famous top-speed numbers often mix burst estimates, hooked-fish observations, and calculations that are not directly comparable.
Do swordfish and sailfish use their bills like spears?
They mainly use rapid slashing, tapping, or sweeping actions to disable prey before swallowing it. Bills can accidentally puncture objects or animals, but spearing is not the safest general description of normal feeding.
Do swordfish and sailfish live together?
Their ocean ranges overlap, especially in warm regions, but swordfish commonly travel through a much wider depth and temperature range. They are wild open-ocean animals and should never be approached, chased, or handled.
Animal Words to Know
- Billfish: A large predatory fish with an elongated upper jaw, including swordfish, sailfish, marlins, and spearfishes.
- Rostrum: A projecting snout or bill at the front of an animal’s head.
- Pelagic: Living in the open-water part of the ocean rather than on the seafloor.
- Caudal keel: A ridge near the base of the tail that helps control water flow around a fast-swimming fish.
- Cranial endothermy: Keeping the brain and eyes warmer than the surrounding water.
Design a Billfish Identification Board
Design a Billfish Identification Board
Draw two calm billfish swimming in the same direction. Give the swordfish a thick cylindrical body, flat broad bill, high short-based dorsal fin, no pelvic fins, smooth adult skin, dark upper body, and crescent tail. Give the sailfish a slimmer compressed body, round bill, enormous spotted dorsal sail, long pelvic fins folded into grooves, small scales, blue bars, and a forked tail. Add arrows for bill cross-section, dorsal-fin length, pelvic fins, scales, teeth, tail keels, deep diving, group hunting, eggs, and larvae. Do not stage a race or point the bills toward people or animals.
Meet Each Animal
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Swordfish Fact Highlight
From the full animal facts pageSailfish Fact Highlight
From the full animal facts pageMore Animal Comparisons
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