Desiccation Resistance in Embryos of the Killifish, Fundulus heteroclitus: Single Embryo Measurements SIRILAK CHUAYPANANG 1 , GEORGE W. KIDDER III 2 , AND ROBERT L. PRESTON 1,2 * 1 School of Biological Sciences, Illinois State University, Normal, Illinois 2 Mount Desert Island Biological Laboratory, Salisbury Cove, Maine The killifish or mummichog, Fundulus heteroclitus, is an estuarine fish inhabiting brackish water and salt marshes along the eastern coast of North America (Bigelow and Schroeder, '53; Able, 2002). Killifish seem to have a vigorous capacity to tolerate various stresses. Adult fish are very efficient osmoregulators that can survive indefinitely in either fresh water (FW) or seawater (SW), and readily tolerate abrupt transfer between FW and SW (Griffith, '74; Atz, '86; Scott et al., 2004a,b, 2005). For this reason, killifish have been a favorite experimental animal in studies that have focused on the physiological and molecular aspects of osmoregulation (e.g., Wood and Marshall, '94; Preston et al., 2003, 2004; Scott et al., 2004a,b; Kidder et al., 2006a,b; ABSTRACT Northern killifish, Fundulus heteroclitus macrolepidotus, spawn in estuaries at high tides. Embryos may be stranded in air at stream margins as the water recedes. These aerially incubated embryos are exposed to desiccation stress and may survive and develop normally to hatching at 14 days post- fertilization (dpf). We developed a technique to quantitatively measure the kinetics of water loss at various developmental stages from single embryos in controlled relative humidities (RHs). Embryos were able to tolerate short periods (2 hr) of severe desiccation and survive to hatching. Mid‐stage (7 dpf) embryos showed the highest degree of desiccation tolerance compared to early‐stage (2 dpf) and late‐stage (14 dpf) embryos. We classified the patterns of water loss into four phases, the perivitelline space (PVS) phase, the resistance phase, the desiccation phase, and the equilibration phase. In the PVS phase, water loss was rapid at all developmental stages and all RHs (25% of total embryo weight). The water loss rate was slower during the resistance phase. It decreased as RH increased and length of this phase was longer in mid‐stage than in early‐ and late‐ stage embryos. The water loss rate and length of the desiccation phase also depended on RH. These data support the hypothesis that low permeability embryonic compartment surface membranes retard water loss significantly and promote prolonged survival of these embryos during desiccation. We also show this mechanism cannot completely account for the survival of severely desiccated embryos (especially in 23% RH) and that there must also be complementary cellular responses. J. Exp. Zool. 319A:179–201, 2013. © 2013 Wiley Periodicals, Inc. How to cite this article: Chuaypanang S, Kidder GW, Preston RL. 2013. Desiccation resistance in embryos of the killifish, Fundulus heteroclitus: single embryo measurements. J. Exp. Zool. 319A:179–201. J. Exp. Zool. 319A:179–201, 2013 Grant sponsor: National Science Foundation (REU); Grant number: CRUI‐ 0111860, DBI‐0453391; Grant sponsor: National Institute of Environmental Health Sciences (STEER); Grant number: 1‐R25‐ES016254‐01; Grant sponsor: National Institutes of Health (INBRE); Grant number: 2‐P20‐RR016463; Grant sponsor: Mt. Sinai School of Medicine, New York (SETH); Grant sponsor: Mount Dessert Island Biological Laboratory (MDIBL); Grant sponsor: Illinois State University; Grant sponsor: The Ministry of Science and Technology of Thailand; Grant sponsor: Thaksin University, Thailand. Additional supporting information may be found in the online version of this article. *Correspondence to: Robert L. Preston, School of Biological Sciences, Illinois State University, Normal, IL 61790‐4120. E‐mail: rlpresto@ilstu.edu Received 22 May 2012; Revised 19 November 2012; Accepted 2 January 2013 Published online 19 February 2013 in Wiley Online Library (wiley onlinelibrary.com). DOI: 10.1002/jez.1783 RESEARCH ARTICLE © 2013 WILEY PERIODICALS, INC.