The Mahi Mahi is a highly sought-after game and food fish, known worldwide for its appearance and powerful swimming ability. Often called Dorado, meaning “golden” in Spanish, or Dolphinfish, this species is a true fish (Coryphaena hippurus) and is entirely unrelated to the marine mammal known as a dolphin. Its reputation as one of the ocean’s fastest creatures is largely due to its remarkable and rapidly changing colors. This combination of speed, size, and coloration makes its appearance instantly recognizable to anglers and enthusiasts across tropical and subtropical seas.
Basic Body Shape and Size
The physical structure of the Mahi Mahi is built for exceptional speed and efficiency in the open ocean. It possesses a compressed, yet muscular, body that is long and streamlined, helping it move quickly through the water. A single, long dorsal fin begins near the head and extends almost the entire length of the fish’s back, a unique feature of the species. This fin, along with its deeply forked tail fin, provides the necessary propulsion and maneuverability for a fast-paced, predatory lifestyle.
While they are among the fastest-growing fish in the sea, their size can vary significantly depending on age and location. The typical size for a commercially caught Mahi Mahi ranges from 15 to 30 pounds. Mature adults can grow to lengths of up to six feet, with the largest individuals recorded reaching weights near 87 pounds.
Vibrant Coloration While Alive
The most striking feature of a living Mahi Mahi is its dynamic coloration, which can shift almost instantly. When actively swimming or excited, the fish displays a dazzling array of colors that seem to shimmer and change as light hits its skin. The back of the fish is typically an electric blue or greenish-blue, contrasting sharply with the sides, which are a brilliant gold or golden-yellow.
Scattered across the flanks are small, irregular spots that can be black or blue. The pectoral fins often exhibit an iridescent blue sheen. This ability to “light up” is controlled by specialized pigment cells called chromatophores, allowing the fish to flash colors for communication or camouflage.
Identifying Differences Between Males and Females
A distinct visual difference, known as sexual dimorphism, separates the male and female Mahi Mahi as they mature. The male, often called a “bull,” develops a prominent, steep, and blunt forehead that gives its head a squared-off profile. This bony crest protrudes significantly above the rest of its body, making the male’s appearance unmistakable. The size of this forehead hump increases noticeably as the bull Mahi Mahi grows older.
In contrast, the female, known as a “cow,” maintains a more rounded and gently sloping head profile. Her head tapers more smoothly from the dorsal fin down to the mouth, lacking the vertical, blunt look of the male. These differences in head shape are the most reliable way to visually identify the fish’s sex.
The Change in Appearance After Capture
The dramatic color change of the Mahi Mahi after it is removed from the water is a famous characteristic of the species. The vibrant blues, greens, and golds begin to fade almost immediately upon capture or death. This rapid transformation is a result of the nervous system losing control over the chromatophore cells in the skin.
As the fish dies, the hues quickly transition through several intermediate colors. Within minutes, this vivid coloration is lost entirely, and the fish settles into a final, muted appearance. The vibrant gold and blue fade to a duller, silvery or muted yellow-gray tone, which is the color most people see when purchasing Mahi Mahi at a market.