The overall measurement of a fish, whether it is fork-tailed or round tailed, is taken from the snout on the upper jaw to the end of the tail.
Abalone are measured along a straight line at the widest point of the shell.
Crabs, except spanner crabs, are measured along the body from the notch between the two most protruding frontal teeth to the centre of the posterior margin of the carapace or shell.
Spanner crabs are measured along the body from the base of the orbital notch (eye socket) to the centre of the posterior margin of the carapace.
Rock Lobsters (crayfish) are measured along the length of the carapace or head, along a straight line from the point of the union of the second antennae or large feelers to the centre of the posterior margin of the carapace or head, ignoring any attached hairs.
Murray Crayfish are measured from the rear of the eye socket to the centre rear of the carapace.