Blue Marlin are generally the most spectacular and the finest fighters of all the marlin species
They have the strength of the black, the agility of the striped and the speed of a white.

A medium size blue marlin in waters of 20 to 26 centigrade (68 to 78 Fahrenheit) and around 500 fathoms will provide as good and long battle as any billfish can give.
Pacific and Atlantic blue marlin are usually found in the warm waters of the equatorial regions.
They are not usually found close to land unless there is a deep drop of 500 to 1 000 fathoms as in the waters of Kona, Hawaii and the Canary Islands.

Blues possess a pair of keels at the caudal peduncle(base of tail) and the tail span is shorter than that of a black marlin.
The first anal fin is the largest in relation to body depth of any other species of marlin being about 70 % as high as the body depth at that point.
The pectoral fin of the blue is slightly convex on the top side with a concave curvature on the bottom, but unlike the black's it will fold back against the body.
The pelvic fins of the blue marlin are almost always over 30 centimeters (12 inches) this is longer than the black's but shorter than that of the striped.

The gill plate is similar to other billfish in position and structure Blues possess vertical stripes of different size and intensity in colour, but these are not as pronounced as those of the striped marlin and often disappear shortly after death, with the body turning a blue-grey colour.
One of the outstanding characteristics of the blue marlin is its body scales which are not firmly fixed to the skin and have three branches.

Their scales are only covered with a very fine layer of skin which make them easily scraped of the body.
Blue marlins of over 909 kilograms (2 000 pounds) has been caught by commercial fishermen and have been recorded up to 820.5 kilograms (1 805 pounds) on rod and reel.

They do not have the depth of body at the shoulder as compared to the black, but blues have more body depth than the striped.

Generally, blue marlin heavier than 136.5 kilograms (300 pounds) are female.
The Pacific and Atlantic blue marlin feed on offshore fish mainly tuna (skipjack).
They have been caught many times with tuna (big eye and yellowfin) 45.5 to 91 kilograms (100 to 200 pounds) in their stomachs.

Like other billfish however, they will eat anything they can catch. They are mainly surface feeders but specimens removed from their stomachs demonstrate they also feed near the bottom. A blue marlin of 1430 lb. (650 kg) was caught in Mauritius on the 23rd November 1984 by I Simonis but not accepted as a world record, due to the fact that it had two lines in it for a few seconds.