One of the most contentious issues I have come across when game fishing is how to differentiate between species of Marlin. A common misconception is if when the fish comes to the boat they are blue or have distinctive stripes that catergorises what they are, WRONG.
There are 3 types of Marlin in Australian waters and they are The Black Marlin, The Blue Marlin and The Stripe Marlin plus we have sailfish,spearfish and broadbill.
I am going to tell you the correct way to tell the Marlin apart.
STRIPED MARLIN. The stripey is a very lean fish compared to its cousins, and its tail is proportionally huge when compared to its body. Its Dorsal Fin is very high and tapers toward the back fin. The Pectoral Fins are long, wide and straight and can fold flat against its body. Its colour is distinctive with very bright blue vertical wide stripes. It has the longest, thinnest bill of all the Marlin. Its flesh is a light salmon colour.
BLACK MARLIN.The Blacks most distinct feature which separates it from its cousins is its Pectoral Fins, they are rigid and curved and do not fold back along the body. Its body is shorter and thicker compared to the others, so is its bill. The colour is dark on top and brightly light on the bottom with a very distinct line between the two. Its Dorsal Fin is a lot shorter than the others and a little more rounded. Its flesh is pale white.
BLUE MARLIN.A Blues most distinctice feature is the shape of its head, its head is a lot higher than the other two fish, though its bill is quite thin. The Dorsal fin has a very fine point compared to the Black, and its Pectoral fins are straight and can close to lay flat along its body. They can present at the boat with bright vertical bars on the body, this does NOT make them Stripeys. They are not only caught in very deep water but are normally fished and caught over the Continental Shelf. Their flesh is pale white. Blues often dive deeper and tire more quickly than the other Marlin.