John Fleng Steffensen

John Fleng Steffensen is a Professor in the Department of Biology within the Faculty of Science at the University of Copenhagen, specializing in Marine Biology. With over 239 research outputs and extensive international collaborations, he maintains an active research program focused on fish physiology. His work spans multiple continents and has been featured in numerous high-profile media outlets including the New York Times, Wall Street Journal, and Le Monde.

Dr. Steffensen earned his M.Sc. in Biology/Zoophysiology from Aarhus University in 1980 and completed his Ph.D. in the same field in 1984. Prior to his current position, he held postdoctoral positions at University of British Columbia (1985), Aarhus University (1986-1988), and served as a Visiting Scientist at University of Miami (1980-1981).

His research primarily focuses on comparative respiratory and circulatory physiology of fish, examining metabolic cold adaptation in Arctic and Antarctic fish species, the benefits and challenges of fish schooling behavior, aquaculture growth improvements, environmental hypoxia and temperature adaptation, swimming metabolism and kinematics, and the form-function relationship of teleost circulatory systems. A significant portion of his recent work has centered on the biology, physiology, and extraordinary longevity of the Greenland shark, which culminated in major media coverage in 2024 regarding the mapping of its genome.

Analysis of Dr. Steffensen's recent publications reveals a strong interdisciplinary approach combining physiology, biomechanics, and conservation biology. His work spans from fundamental physiological mechanisms to applied conservation questions, with particular emphasis on how fish respond to environmental stressors like warming oceans and hypoxia. The Greenland shark longevity research represents a major contribution to understanding extreme lifespan in vertebrates.

• American Fisheries Society, Physiology Section. Award of Excellence (2022)

Dr. Steffensen has been actively involved in numerous research networks and collaborative projects, including the EU Cost Action FA1303 FitFish (2015-2018), TUNU-Programme on Marine Fishes of NE Greenland (2007-2015), and MADFISH (Molecular Adaptations of FISH). He has organized significant training courses including the FitFish Training Course in Respirometry and the MadFish Respiratory and Circulatory Fish Physiology PhD-course. His research has received considerable attention, with his 2016 Science paper on Greenland shark longevity accumulating over 245 citations and extensive media coverage.

Dr. Steffensen maintains the Marine Biology Laboratory (MBL) at the University of Copenhagen, where his team conducts research on fish physiology using advanced respirometry systems and molecular techniques. His lab has been instrumental in developing methods for studying fish metabolism and has contributed significantly to our understanding of how fish adapt to extreme environments.