Despite extensive research into thermal relationships of ectothermic animals, there remain large gaps in our understanding of how temperature affects the ability of ectotherms to cope with pathogens through both specific and nonspecific immune responses. Temperature affects both specific and nonspecific immunity, so these thermal effects are apt to be of considerable importance to ectotherms that encounter variations in environmental temperature (see Le Morvan et al., 1998 for a review). Low temperatures, consistent with normal seasonal fluctuations, correlate with increased pathogenesis in teleost fish (Baudouy et al., 1980; Bly and Clem, 1992; Le Morvan et al., 1998). Most infectious diseases occur over wide ranges of body temperatures and the outcome of the pathogenesis is likely to depend on the differential effects of change in temperature on the efficacy of the immune response and the growth rate of the pathogen. In 4539 The Journal of Experimental Biology 206, 4539-4551 © 2003 The Company of Biologists Ltd doi:10.1242/jeb.00706 The ability to heal superficial wounds is an important element in an organism’s repertoire of adaptive responses to environmental stress. In fish, motile cells termed keratocytes are thought to play important roles in the wound-healing process. Keratocyte motility, like other physiological rate processes, is likely to be dependent on temperature and to show adaptive variation among differently thermally adapted species. We have quantified the effects of acute temperature change and thermal acclimation on actin-based keratocyte movement in primary cultures of keratocytes from four species of teleost fish adapted to widely different thermal conditions: two eurythermal species, the longjaw mudsucker Gillichthys mirabilis (environmental temperature range of approximately 10–37°C) and a desert pupfish, Cyprinodon salinus (10–40°C), and two species from stable thermal environments, an Antarctic notothenioid, Trematomus bernacchii (–1.86°C), and a tropical clownfish, Amphiprion percula (26–30°C). For all species, keratocyte speed increased with increasing temperature. G. mirabilis and C. salinus keratocytes reached maximal speeds at 25°C and 35°C, respectively, temperatures within the species’ normal thermal ranges. Keratocytes of the stenothermal species continued to increase in speed as temperature increased above the species’ normal temperature ranges. The thermal limits of keratocyte motility appear to exceed those of whole-organism thermal tolerance, notably in the case of T. bernacchii. Keratocytes of T. bernacchii survived supercooling to –6°C and retained motility at temperatures as high as 20°C. Mean keratocyte speed was conserved at physiological temperatures for the three temperate and tropical species, which suggests that a certain rate of motility is advantageous for wound healing. However, there was no temperature compensation in speed of movement for keratocytes of the Antarctic fish, which have extremely slow rates of movement at physiological temperatures. Keratocytes from all species moved in a persistent, unidirectional manner at low temperatures but at higher temperatures began to take more circular or less-persistent paths. Thermal acclimation affected the persistence and turning magnitude of keratocytes, with warmer acclimations generally yielding more persistent cells that followed straighter paths. However, acclimation did not alter the effect of experimental temperature on cellular speed. These findings suggest that more than one temperature- sensitive mechanism may govern cell motility: the rate- limiting process(es) responsible for speed is distinct from the mechanism(s) underlying directionality and persistence. Keratocytes represent a useful study system for evaluating the effects of temperature at the cellular level and for studying adaptive variation in actin-based cellular movement and capacity for wound healing. Key words: Antarctic fish, cell motility, cytoskeleton, notothenioid, keratocytes, temperature. Summary Introduction Influences of thermal acclimation and acute temperature change on the motility of epithelial wound-healing cells (keratocytes) of tropical, temperate and Antarctic fish Rachael A. Ream 1 , Julie A. Theriot 1 and George N. Somero 2, * 1 Biochemistry Department, Beckman Center, Room 473A, Stanford University School of Medicine, Stanford, CA 94305-5307, USA and 2 Hopkins Marine Station, Pacific Grove, CA 93950, USA *Author for correspondence (e-mail: somero@stanford.edu) Accepted 4 September 2003