The question of what animal is the best swimmer does not have a single answer, as the term “best” depends entirely on the metric used for comparison. The champions of the aquatic world specialize in different areas, whether they are focused on pure velocity, extreme diving depth, or long-distance endurance. There are distinct record holders for each category, demonstrating the diverse paths evolution has taken to conquer the challenges of moving through water.
The Title Contenders: Speed Records
The most common interpretation of “best” swimmer relates to maximum speed, a competition dominated by the sleek, powerful fish of the open ocean. The sailfish is widely recognized as one of the fastest aquatic animals, with recorded bursts of speed reaching approximately 68 miles per hour (110 km/h). This velocity is achieved through a rigid, lunate (crescent-shaped) caudal fin, which provides highly efficient thrust, and a specialized bill that minimizes resistance.
The black marlin is another top contender for the speed crown, with some reports suggesting it can reach speeds of up to 82 miles per hour (132 km/h) in short bursts. Like the sailfish, the marlin possesses a highly hydrodynamic, torpedo-like body shape that minimizes drag. These billfish utilize their rigid pectoral and pelvic fins, which they can retract into grooves on their body to create a streamlined profile during high-speed chases.
The shortfin mako shark is also a remarkable speedster, capable of reaching speeds around 45 miles per hour (72 km/h), making it the fastest shark species. The mako’s speed is aided by its endothermy, a rare trait among fish that allows it to maintain a body temperature higher than the surrounding water. This elevated temperature provides the necessary power and energy for the rapid muscle contractions required for explosive acceleration and swift movements.
The Endurance and Depth Specialists
While speed defines one category, other champions excel in the metrics of endurance and extreme depth. The Cuvier’s beaked whale holds the record for both the deepest and longest dives documented for any mammal. One individual was recorded diving to a depth of 2,992 meters (9,816 feet), and another stayed submerged for 222 minutes.
To withstand the immense pressure and lack of oxygen at these depths, these whales employ several physiological mechanisms. They exhale up to 90% of their air before a deep dive, which helps to collapse their lungs and minimize the absorption of nitrogen into the bloodstream, preventing decompression sickness. They also possess high concentrations of myoglobin in their muscles, a protein that effectively stores oxygen for use during extended periods underwater.
The Southern elephant seal is another deep-diving specialist, regularly reaching depths greater than 1,500 meters and remaining submerged for hours. Both elephant seals and beaked whales utilize a dive response that includes bradycardia, or a significantly slowed heart rate, to conserve their limited oxygen supply. This suite of adaptations allows them to manage their oxygen stores for incredible feats of endurance.
Biological Engineering for Aquatic Movement
The success of all aquatic champions relies on fundamental biological engineering principles that minimize resistance and maximize propulsive force. A primary goal is reducing drag, which is achieved through a highly streamlined, or fusiform, body shape that is tapered at both the head and tail. This design promotes laminar flow, where water glides smoothly over the surface rather than creating turbulent, energy-wasting eddies.
Many fast species have evolved specialized surface textures that further reduce friction drag. Sharks, for instance, have microscopic, tooth-like scales called dermal denticles that create micro-grooves, or riblets, which redirect water flow. This non-smooth surface helps delay the transition from laminar flow to chaotic turbulent flow, allowing the animal to cut through the water more efficiently.
Propulsion is generated by the caudal fin, and the most efficient shape for high speed is the stiff, high-aspect ratio lunate tail seen in marlins and tuna. This shape moves side-to-side like a flapping wing, generating massive thrust with minimal drag. Other creatures, like dolphins, use a distinct up-and-down motion of their horizontal tail flukes, which, combined with their ability to tuck their appendages, creates a nearly perfect torpedo shape for sustained speed and maneuverability.