Goodness of fit (R²) of regression between degree-day sum (D) and standard length increment (ΔL) in relation to the threshold water temperature (T_threshold) in tagged common carp (o; n = 684) and pikeperch (Δ; n = 513) in Lake Balaton. For reference, R² values of the regression between calendar days and ΔL are indicated by horizontal lines (∙   ∙   ∙   ∙  in common carp and − ∙ - ∙  in pikeperch), while the vertical line (- − −) represents the set T_threshold.