Mahi-mahi are swift and acrobatic game fish with striking colours. Their sides are golden with iridescent greens and blues, and their belly is white and yellow. These colours can change rapidly, excited fish "light up", and dying mahi-mahi often turn silvery over-all with blue spots on the flanks. These colours darken when the fish dies (see illustrations) The current IGFA all tackle record is 39.91 kilograms (88lb), caught in 1998 in Exuma, Bahamas. Catches average 7 to 13 kilograms (15 to 29 lb), and any mahi-mahi over 18 kilograms (40 lb) is exceptional. Males are larger than females.
Mahi mahi are also known as dorado or dolphin fish. However, they are not at all related to dolphins. Dolphins are space-breathing mammals, whereas mahi mahi are water-breathing fish, distantly related to perch. They are good food fish, similar to flounder, tilapia and other whitefish.
Mahi-mahi are a blue-water, open ocean, highly migratory schooling fish found around the world in tropical and subtropical waters at depths up to 85 metres (279 ft), but more typically near 37 metres (121 ft). They feed on forage fish, such as mackerel and squid, and also zooplankton and crustaceans. They are particularly adapted to hunting flying fish.
They spawn in warm ocean currents throughout much of the year, and their young are often found among seaweed. They are a relatively short lived species, with a life span of only four or five years. Mahi-mahi are among the fastest growing fish, with a minimum population doubling time under 15 months. This makes them resilient to fishing pressure. However, their current vulnerability is moderate to high.
In earlier years, most mahi-mahi were caught accidentally, as bycatch in tuna and swordfish longline commercial fisheries. Now they are sought by both commercial and recreational fishermen.
A typical fishing technique is to take a sport fishing boat to the edge of a reef in about 120 feet (37 m) of water and troll near a line of floating sargasso weed . Mahi-mahi often congregate around marine debris such as floating boards, palm trees and fronds, often found in association with such weed lines. Sargasso sometimes holds a complete ecosystem from microscopic creatures to seahorses, small crabs, juvenile triggerfish and other bait fish. Frigate birds dive for the food accompanying the debris or sargasso. Other fish may be present in the area. Experienced fishermen can tell what species are likely around the debris by the birds' behaviour.
Mahi-mahi typically are taken by trolling ballyhoo on the surface with 30 to 50 pound line test tackle. Once a school of Mahi are encountered, casting with small jigs or Fly casting using a bait-and-switch technique can be successful. Ballyhoo or a net full of live sardines tossed into the water can be used to excite the mahi-mahis into a feeding frenzy. Hookless teaser lures can also be employed in the same manner. The teasers or live chum are tossed into the water, the fly is thrown to the feeding mahi-mahi. Once hooked, mahi-mahi are acrobatic game fish displaying spectacular blue, yellow and green colours