Adult nfe2^−/−zebrafish demonstrate decreased ability to spread on fibrinogen. Whole blood was collected from adult zebrafish and applied to glass coverslips pretreated with fibrinogen. Thrombocytes were identified on the basis of Tg(cd41:egfp) fluorescent expression. Images were captured 30 minutes after application of whole blood and analyzed for degree of spreading. The following panels are representative of the scoring system for the spreading assay: images were scored as 1, no spreading (A-C); 2, spreading initiated, but incomplete (D-F); and 3, complete spreading (G-I) by an observer blinded to genotype. Scale bars, 10 μm. Percentages of thrombocytes displaying each score were tabulated for nfe2^+/+ and nfe2^−/− fish, and mutant fish displayed a significant decrease in spreading compared with wild-type siblings (J; P < .0001). Total thrombocyte area was also quantitated using ImageJ and demonstrated a statistically significant reduction in thrombocyte spreading in mutant fish as well (K; P < .0001). Each point represents the area of an individual thrombocyte. Data were collected from a total of 4 fish for each genotype.