Fish measurement is the measuring of individual fish and various parts oftheir anatomies, for data used in many areas ofichthyology, includingtaxonomy andfishery biology.
Standard length (SL) is the length of a fish measured from the tip of the snout to the posterior end of the last vertebra or to the posterior end of the midlateral portion of thehypural plate. This measurement excludes the length of thecaudal (tail) fin.[1]
Total length (TL) is the length of a fish measured from the tip of the snout to the tip of the longer lobe of the caudal fin, usually measured with the lobes compressed along the midline. It is a straight-line measure, not measured over the curve of the body.[2]
Standard length measurements are used withTeleostei (mostbony fish), while total length measurements are used with Myxini (hagfish), Petromyzontiformes (lampreys) and usuallyElasmobranchii (sharks andrays), as well as some other fishes.[2]
Total length measurements are used inslot limit andminimum landing size regulations.
Fishery biologists often use a third measure in fishes with forked tails, calledFork length (FL), the length of a fish measured from the tip of the snout to the end of the middle caudal fin rays, and is used in fishes in which it is difficult to tell where the vertebral column ends.[3]
Other possible measurements include the lengths of various fins, the lengths of fin bases and the diameter of the eye.[4]
