A Simple Method for Predicting Hatch Date in the Field

Lab and hatchery data show a clear relationship between egg development and incubation temperature in fish. Although this relationship is useful for predicting hatch date when incubation temperature is relatively constant, it is of little use when incubation temperature is variable (e.g., in flow-through hatcheries or the wild). In this study, we use published data for dozens freshwater and anadromous fishes to estimate the cumulative degree-days (CDD; ^oD) at which eggs are predicted to hatch for almost any temperature regime. We estimated CDD at hatch as CDD = (T_i – T_m) x D, where T_i is incubation temperature, T_m is the minimum T_i for egg development and D is days to hatch. We estimated T_m by finding the x-intercept of the relationship between development rate (1/D) and T_i. For a subset of the species in our database, we used published field data to test the predictive ability of the CDD model. Our results suggest that CDD accurately predict hatch date in the field provided that T_i, oxygen, and salinity are within tolerable limits.