We hypothesized that NOD mouse β cells expressing solely Seriola dumerili Ins2 (mouse Ins1−/−, mouse Ins2−/−, fish Ins2+/+) would be less diabetes-prone by virtue of glutamic acid to aspartic acid substitutions at aa13 and aa21 in Seriola dumerili Ins2 vs. human insulin in the region of the Β chain essential for immune tolerance to insulin (Fig. 1A). The gene discussed is INS; the disease is diabetes mellitus.