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Mahi mahi are known for their spectacular colors

By Staff | Aug 29, 2019

According to The Oxford English Dictionary, the first recorded use of the word “dolphin” for the fish may have been in 1627, when Capt. John Smith reported using hooks to catch dolphins, or dorados.

The dolphinfish (dorado, mahi mahi) is so spectacularly colorful that it seems impossible that it could have evolved by accident. The back and head are iridescent, glowing neon blue and chartreuse green. The sides are gold sprinkled with a mixture of bright blue and black spots. The belly is a silvery-white or yellow. The dorsal fin is rich blue. These are the natural colors of the fish and are apparently maintained during normal undisturbed activity.

Like some other pelagics, the mahi mahi has the ability to “light up” with shimmering waves of color across its body, almost as if its skin were embedded with moving lights. This change in color is accomplished by the myriad chromatophores (color cells) in the skin of the fish.

Chromatophores containing blue, green, yellow, brown and other pigments are capable of alternately expanding and contracting, being so closely crowded together that as certain ones contract and others expand, the effect will be a sudden or gradual change in the hue of the fish.

In fact, biologists say the fish’s color is the result not only of pigment, but also of microscopic structures in the skin, which the fish can manipulate to change its color. The color changes could have evolved for spawning selection, or perhaps as a camouflage when approached by predators.

Anyone who has fished for mahi will recall the remarkable play of colors, which takes place in the fish’s skin as it dies. After death, all the chromatophores tend to contract almost instantly, leaving the fish an ugly, pale grayish-brown or dull yellow in color.

Because mahi are sexually productive at an early age and are so fast growing, the popular scientific theory is that this species can withstand a high rate of exploitation. All mahi can reproduce by three to five months of age or 22 inches in length.

Once the fish reach maturity, the spawning season for mahi is long, and multiple spawnings every six weeks are common in both males and females, broadcasting about 400,000 eggs.

The eggs, which are about the size of the head of a pin, hatch in about 60 hours. The little fish start growing immediately. Mahi spawn in pairs, rather than communally, with spawning occurring year-round In Hawaiian waters.

At five months, they can reach 5-6 pounds and are mature. At one year, most exceed 20 pounds. Three-year-olds usually exceed 30 pounds. Few fish live beyond the fourth year, if any make it past five years. Eighty-five percent of all mahi die during their first year.

The Hawaii state record is 82 pounds caught in Kona. The Lahaina Harbor record is 77.6 pounds. These fish were probably around four years old.

Pacific mahi are opportunistic feeders. Most people think of mahi as surface animals, but data has verified that they feed throughout the water column, just like billfish do. They eat everything from paper nautilus to their number one dietary preference: flying fish (malolo) and opelu (mackerel scad).

They also feed both at night and during the day. They have been documented to diving to 400 feet at night to feed. Data also confirms that the majority of fish spend 50-80 percent of their time within the top 30 feet of the water column.