The Big-Eye Trevally (Caranx sexfasciatus) is undoubtedly the most abundant, locally occurring member of Carangidae family, which also includes the Jack Mackerels, Pompanos and Scad.
The Big-Eye Trevally differs from its close relatives in that it is a primarily nocturnal hunter and also because it often forms huge schools during the daytime.
These traits are in sharp contrast to other members of the genus Caranx which tend to form very small, but highly active hunting groups during the daytime.
Although reportedly growing to a maximum length of well over 1m, by far the most common size range for local individuals would likely be from 20 - 50cm.
The Big-eye Trevally is one of the most easily recongnised member of its family, due not only to its schooling behaviour, but also its overall appearance.
Adults are almost completely silver, with the exception of the white tip on the second dorsal fin and a small black spot on the gill cover (operculum).
At times when spawning occurs, individuals may be seen breaking away from the main group as pairs, with one individual temporarily changing colour to a slate gray to almost black, although as yet i'm not sure if it is the male or female that changes colour.
As a result of their mainly nocturnal hunting behaviour they have, as the common name suggests, large eyes when compared to other members of the genus.
Although small numbers of sub-adults may be found around local inshore reefs, they are far more abundant at the deeper offshore sites such as Chumphon Pinnacles & South West Pinnacles and in particular Sail Rock where their schooling behaviour provides some spectacular diving.