Euryhaline Elasmobranchs

• Published in: Fish Physiology Vol. 32; pp. 125 - 198
• Main Authors: Ballantyne, J.S., Fraser, D.I.
• Format: Book Chapter
• Language: English
• Published: Elsevier Science & Technology 01.01.2013
• Subjects: elasmobranch; euryhaline; fish; freshwater; metabolism; salinity; sensory; shark; shark; salinity; sensory; fish; metabolism; elasmobranch; freshwater; euryhaline
• ISBN: 0123969514; 9780123969514
• ISSN: 1546-5098; 1557-8011
• DOI: 10.1016/B978-0-12-396951-4.00004-9

This chapter explores the physiology of freshwater, marine, and euryhaline elasmobranchs. In seawater, the blood of elasmobranchs is slightly hyperosmotic and the need for water balance is limited. Salt balance is handled partly by a rectal gland that removes salt from the plasma and secretes it into the rectum for elimination. In freshwater this gland is non-functional, and salt balance is handled by gill uptake mechanisms and kidney retention. A significant portion of plasma and cellular osmolarity in seawater is comprised of organic solutes, e.g. urea. The small number of freshwater and euryhaline elasmobranch species may be explained by several factors, including: the osmoregulatory system (rectal gland cannot reverse its function in freshwater); temperature (freshwater distribution limited to warmer latitudes), reproductive and sensory limitations (reduced electroreception in freshwater); and the use of urea as the main organic osmolyte in seawater (may be limiting in freshwater). Further studies of euryhaline elasmobranch physiology and biochemistry are needed to fully understand the scarcity of these species.