Mar. Fresh. Behav. Physiol., Vol. 31, pp. 55-61 Reprints available directly from the publisher Photocopying permitted by license only © 1998 OPA (Overseas Publishers Association) Amsterdam B.V. Published under license under the Gordon and Breach Science Publishers imprint. Printed in India. Short Communication VISUALIZATION AND QUANTIFICATION OF BIOLOGICAL FLOW FIELDS THROUGH VIDEO-BASED DIGITAL MOTION-ANALYSIS TECHNIQUES* THOMAS BREITHAUPT a, * and JOSEPH AYERS b a Fakultät für Biologie, Universität Konstanz, Postfach 5560 (M618), D-78457 Konstanz, FRG; b Marine Science Center, Northeastern University, East Point, Nahant, MA 01908, USA (Received 28 February 1997; In final form 23 April 1997) Keywords: Flow visualization; digital image processing; particle tracking velocimetry; exopodite currents; Procambarus clarkii; Crustacea The study of the water currents surrounding aquatic animals and the behav- ior associated with these currents yields a great deal of insight into crucial aspects of the life of aquatic animals. Many behaviors, e.g. locomotion, breathing, filter feeding, odor communication, chemo- and rheotactic orien- tation, can only be understood with a knowledge about the water currents surrounding the animal. Various techniques have been used so far by biol- ogists to visualize flow pattern in water (for references see Breithaupt and Ayers, 1996). Only recently, new quantitative techniques, Particle Tracking Velocimetry (PTV) and Particle Image Velocimetry (PIV), using digital image processing were introduced into the field of biology (Stamhuis and Videler, 1995). These techniques are based on the analysis of the displacement of *This paper is accompanied by animation on the MFBP web site: http://www.gbhap.com/journals/142/142-top.htm. * Corresponding author. Fax: 49-7531-883018. E-mail: thomas.breithaupt@uni-konstanz.de. 55