Abstract
The fasting state of marine mammals is of interest to the scientific community, including the ability for Northern elephant seals to fast for months1 and bottlenose dolphins to develop diabetes-like changes during overnight fasting.2 Previous acute fasting (36–72h) and re-feeding studies among dolphins have shown that dolphins are not 'fasting adapted'; changes in feeding hormones closely mimic what has been reported in humans and rats versus that found in long-term fasting marine mammals.3 To better understand the physiology of short-term fasting versus feeding in dolphins, hourly blood and urine creatinine, creatine, sodium, chloride, and urea; and urine volume were measured over 24h following 12h of fasting; in addition to the fasting study, feeding studies included ingestion of Spanish mackerel or 10% dextrose in Ionosol. Clearance rates were calculated. Compared to ingestion of mackerel and dextrose, the fasting state was more likely to stimulate lower urine flow rates and higher urine creatinine concentrations (36, 172, 802 mg/dl, respectively) and creatine concentrations (75, 14, 359 mg/dl, respectively), leading to higher creatinine clearance rates (185, 228, 441 ml/min, respectively) and creatine clearance rates (171, 12, 407 ml/min, respectively). These data support that dolphins may readily pull from muscle-based protein reserves to support even short-term fasting (24–36h). Further studies are needed to assess the clinical relevance, if any, of shorter, routine overnight fasting (12–14h) among dolphins in managed collections and longer term fasting due to decreased prey availability among wild dolphins.
Acknowledgements
The authors thank Mr. Christopher Hammell at the National Marine Mammal Foundation for developing the study's database.
References
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