There are different ways of measuring lengths in fish:

Fork length: from snout to beginning of fork of the caudal fin.

Head length: from snout to the end of theoperculum.

Standard length: from snout to caudal peduncle.

Total length: from snout to the end of the caudal fin with its filaments.

Alternative forms for length : fork length (FL), head length (HL), standard length (SL), total length (TL).