Freezing response and optimal cooling rates for cryopreserving sperm cells of striped bass, Morone saxatilis S. Thirumala a , W.T. Campbell b , M.R. Vicknair c , T.R. Tiersch b , R.V. Devireddy a, * a Bioengineering Laboratory, Department of Mechanical Engineering, Louisiana State University, Baton Rouge, LA, USA b Aquaculture Research Station, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA, USA c Kent SeaTech Corporation, 11125 Flintkote Avenue, Suite J, San Diego, CA, USA Received 31 October 2005; accepted 7 February 2006 Abstract This study explored the optimization of techniques for sperm cryopreservation of an economically important fish species, the striped bass Morone saxatilis. The volumetric shrinkage or the water transport response during freezing of sperm cells was obtained using a differential scanning calorimeter (DSC) technique. Water transport was obtained in the presence of extracellular ice at a cooling rate of 20 8C/min in two different media: (1) without cryoprotective agents (CPAs), and (2) with 5% (v/v) dimethyl sulfoxide (DMSO). The sperm cell was modeled as a cylinder of length of 22.8 mm and diameter 0.288 mm and was assumed to have an osmotically inactive cell volume (V b ) of 0.6V 0 , where V 0 is the isotonic or initial cell volume. By fitting a model of water transport to the experimentally determined water transport data, the best fit membrane permeability parameters (reference membrane permeability to water, L pg or L pg [cpa] and the activation energy, E Lp or E Lp [cpa]) were determined and ranged from L pg = 0.011–0.001 mm/min-atm, and E Lp = 40.2–9.2 kcal/mol). The parameters obtained in this study suggested that the optimal rate of cooling for striped bass sperm cells in the presence and absence of DMSO range from 14 to 20 8C/min. These theoretically predicted rates of optimally freezing M. saxatilis sperm compared quite closely with independent and experimentally determined optimal rates of cooling striped bass sperm. # 2006 Elsevier Inc. All rights reserved. Keywords: Differential scanning calorimetry; Water transport; Reference membrane permeability and activation energy 1. Introduction Four economically important species of the genus Morone are cultured in the United States. White perch (Morone americana) is a brackish water species but also inhabits fresh water lakes and reservoirs. White bass (M. chrysops) and yellow bass (M. mississippiensis) are restricted to freshwater environments, whereas striped bass (M. saxatilis) is anadromous. Also, the hybrid (HB) of M. chrysops  M. saxatilis, although generally stocked into freshwater systems, does well in a wide range of salinities from 0 to 25 ppt. The genus Morone provides a highly desired sport fish in freshwater and brackish impoundments, and several hatcheries for artificial propagation of these species and hybrids provide seedstock for fisheries and for commercial aquaculture. The impetus for the research reported here, directed toward cryopreservation of striped bass spermatozoa, is aimed at enhancing our predictive www.journals.elsevierhealth.com/periodicals/the Theriogenology 66 (2006) 964–973 * Corresponding author. Tel.: +1 225 578 5891; fax: +1 225 578 5924. E-mail address: devireddy@me.lsu.edu (R.V. Devireddy). 0093-691X/$ – see front matter # 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.theriogenology.2006.02.035