abbreviation for standard length
the measurement from the most anterior tip of the body to the midlateral posterior edge of the hypural plate (in fish with a hypural plate) or to the posterior end of the vertebral column (in fish lacking hypural plates). It may be restricted to the tip of the snout if the lower jaw projects. The base of the caudal fin (end of the vertebral column or posterior edge of the hypural plate) is determined by flexing the tail up while the caudal peduncle is held down. The resultant wrinkle or caudal flexure indicates the caudal base. It may also be determined by probing or dissection. Sometimes the posteriormost point is the last scale, the last pored scale or the beginning of the caudal fin rays. It is the usual scientific measurement for length of a fish except in Amphioxi, Myxini, Petromyzontiformes, Elasmobranchii and Holocephali. This measurement is used because long-preserved fish often lose the tips of the caudal fin rays through breakage after the desiccation effect of alcohol. See total length and fork length. In Holocephali the length is usually taken from the tip of the snout to the origin of the upper caudal fin because the caudal filament breaks off frequently. In Scaridae it is taken back to the rear margin of the second to last lateral line scale {because the large scales obscure the point of caudal flexure. Also abbreviated as sl or Sl.)

Dictionary of ichthyology. 2009.

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