Maximum size attained by great barracuda is debatable. Interestingly, the purported size of specimens in old accounts of natural history and exploration became smaller as the twentieth century approached. Labat asserted, in 1724, that the beast grew to lengths of 5.5 to 6 m in the Caribbean area, from which we see a gradual progression to Vincent's 1910 claim of 2.6 m. Behemoths of 2.5 m or so may exist, but are probably rare. It must be remembered when listening to others' stories that barracuda tend to grow exponentially between the time they escape the hook of an angler and the time they are described at the tiki bar that night. Anything over 1.5 m long is a very large 'cuda, particularly given that their overall mass continues to increase greatly once they have attained a certain length. Weight is not something that I deal with very much — the nature of my research thus far has me concerned with estimating body lengths, as observed in the field — but de Sylva mentions in his 1963 paper that the world record for a hooked great barracuda was for a fish almost 1.7 m in length that weighed almost 47 kg. This fish's proportions illustrate quite well how the barracuda continues to grow more in girth than length as it ages. The current International Game Fish Association (IGFA) official world record is for a great barracuda — caught in 1992 in the Central-Pacific Republic of Kiribati — that weighed 38.6 kg. This figure is obviously lower than the 50 kg typically mentioned as the species' maximum weight (at least one hook-and-line record exists, from the Bahamas, of a 1.7-m-long great barracuda that weighed 46.7 kg) but certain criteria have to be met for a fish to become an IGFA record-holder. Besides, fishing with hook and line is not necessarily going to land the biggest fish out there.

Juvenile great barracuda can closely match their background, a trait that enhances survival as much as foraging success. The entire body can pale to match sand, or take on a brownish or olive green mottled appearance conferred by alternating irregular dark and light dorsal bars. This pattern, that bears some resemblance to US Marine Corps standard camouflage, makes young barracuda very hard to see amongst turtle grass or against other dark backgrounds. The barred pattern also mimics the patterns created by dappled light that are characteristic of shallow water where sunlight plays on small waves. The barracuda's shading and pattern changes are instantaneous in transition.

The same patterns and shades can be seen in adults, as well as a characteristic overall blackening and the highly reflective overall silver (stainless steel or 'mirror') variant of the usual countershaded silver scheme. Adults appear to be generally more silver than juveniles — advantageous to a fish that often hovers in mid-water or near the surface but possibly a disadvantage to the survival of juveniles in vegetated habitats.

A very interesting phenomenon is the ability of great barracuda to selectively darken or lighten their lateral blotches. I first noticed this when, while attempting to record the spot patterns of a barracuda on my slate, I looked up to see that the markings I had drawn had all but disappeared. This fading of lateral blotch markings seems to be under selective control — indicating that the barracuda can turn particular spots or groups of spots on and off at will — and is independent of any overall color change, fading, or darkening. This phenomenon may be an example of a communication system previously unsuspected in these or any other fishes.

The speed of the great barracuda has been estimated as 40-58 kph, that would perhaps surprise many who see the great barracuda only as it drifts subtly by at slow speed. The great barracuda can move forward at a very slow speed without any perceptible effort, that enhances its ability for stealth even while cruising in the transparent openness of mid-water.