Fig. 1

Blood glucose and ketone levels under the control diet (CD) or ketogenic diet (KD). A Experimental procedure. After fish were raised for 3–4 months on a brine shrimp larva diet, fish were fed the CD or KD for 5 weeks. Blood glucose and ketone levels were measured after the 5-week period. B Blood ketone level (mmol/L). Ketone levels were significantly reduced by KD feeding in both surface fish (SF) and cavefish (CF). Bars represent the data mean and whiskers represent ± standard error of the mean. Dots indicate individual data. The generalized linear model (family = Poisson) followed by post hoc Holm’s correction was applied for the statistical tests (see “Methods” and Additional file 3). C Blood glucose level (mg/dL). Glucose levels were significantly reduced by KD feeding in both SF and CF. The linear model (family = Gaussian) followed by post hoc Holm’s correction was applied for the statistical tests. D The glucose ketone index (GKI) indicated that the ratio of glucose to ketone was lowered by KD feeding in both SF and CF, suggesting that this diet altered the balance between glucose and ketone. The generalized linear model (family = Gamma) followed by post hoc Holm’s correction was applied for the statistical tests. SF: N = 13 for CD feeding, N = 8 for KD feeding. CF: N = 13 for CD feeding, N = 11 for KD feeding. *: P < 0.05, **: P < 0.01, ***: P < 0.001. All detailed statistical data are available in Additional file 3