Ask Dr Dazza: All you need to know about Mahi Mahi

Mahi mahi or dolphin fish are prized table and sport fish for the offshore angler and one of the most colourful pelagic fish you will encounter.

There are two species of mahi mahi present in Australia – the common mahi mahi (Coryphaena hippurus) characterised by its vivid yellow colouration, and the less colourful and rarely encountered pompano mahi mahi (Coryphaena equiselis).

Mahi mahi are widely distributed across oceans globally. In Australia, they can be caught at least seasonally in all mainland states and there are even instances where they have been caught in Tasmanian waters. They are highly migratory with water temperature considered to be a key driver of their movements. They prefer waters between 21 and 30 degrees Celsius. Although they can be found in coastal waters, they are principally a fish of offshore waters.

Open ocean surface waters are big and can be lonely places for a fish. Several species of pelagic fish are attracted to and aggregate around floating objects in the water such as rafts of seaweed. Mahi mahi are one such species. Mahi mahi associated with floating objects spend more than 95 per cent of their time in the first 10m below the object at the sea surface.

To take advantage of this behaviour, fish aggregating devices or FADs are deployed and there a series of offshore FADs put in place by the Queensland Department of Primary Industries from Gold Coast to the Sunshine Coast and Wide Bay. FADs are surface or subsurface structures which are moored in place.

FADs are thought to provide a refuge for juvenile fish and bait fish, but also create a visual stimulus that fish such as mahi mahi use to hang out. Simply, FADs are like a pub for mahi mahi where they meet up with mates, have a feed and find potential partners.

It is easy to tell larger male and female mahi mahi apart. Males are called “bulls” which have a very pronounced and flattened forehead, while the females are called “cows” and have a more rounded and tapered heat. FADs generally have larger concentrations of females than males, with the very large males considered to spend more time away from FADs.

Mahi mahi are exceptionally fast-growing fish, one of the fastest growing overall. They can reach about 1kg after only six months and an amazing 10kg in one year. They have generally reached sexual maturity at six months of age. They are a short-lived species which only live to about four years of age. They pack a lot of living into their short lives and can reach a maximum length of 2m!

Mahi mahi feed are opportunistic feeders and feed on a large variety of small fish and larger planktonic animals. Mahi mahi are themselves prey for larger pelagic fish including tunas, marlin and sailfish.

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