Serum triglycerides and ß-hydroxybutyrate predict feeding status in green turtles (Chelonia mydas): Evaluating a single blood sample method for assessing feeding/fasting in reptiles

The foraging success or feeding rate of an animal is important information for ecologists and wildlife managers but can be difficult to assess, particularly in marine vertebrates that are hard to follow at sea. Here we evaluate a method for determining recent feeding history using a single blood sample by measuring the concentration of relevant serum metabolites. Five captive green turtles were either fed a maintenance diet or subjected to fasting periods ranging from 5–15 days. Serial serum samples were collected during both fed and fasted periods, and we determined triglyceride, ß-hydroxybutyrate, and glycerol concentrations using spectrophotometric assays. Serum triglyceride and glycerol concentrations decreased during fasting periods, while serum ß-hydroxybutyrate concentration increased during fasts. For triglyceride and glycerol, this decrease apparently occurred in the first 5 days of fasting and was unaltered by further fasting. ß-hydroxybutyrate concentration continued to increase during longer fasting periods. The decrease in serum glycerol was unexpected and may be due to metabolic down-regulation in fasted turtles. Serum triglyceride and ß-hydroxybutyrate appear to be good indicators of feeding state and can be applied to wild turtles.

► We sampled plasma from fed and fasted green turtles.
► Plasma triglyceride and glycerol concentrations were lower during fasting.
► Plasma ß-hydroxybutyrate concentration was higher during fasting.
► These metabolites can be used to determine recent feeding history in turtles.