Abstract

The importance of calcium (Ca) and phosphorus (P) in reptile diets has been the subject of much research, as chronic imbalances may lead to diseases such as Metabolic Bone Disease (MBD). Nutritionally related MBD results from chronic consumption of diets low in Ca and sometimes vitamin D3, and diets high in P. Some research suggests that sea turtles may be more tolerant of diets with elevated P content and Ca: P ratios < 1 than other reptiles. Long term plasma elevations in P and inverted Ca: P ratios have not been adequately investigated in sea turtles, though it is not uncommon to encounter such chemistry values in captive or rehabilitating animals. Dietary guidelines specifically for sea turtles, either in captivity or rehabilitation, have not been formally established, though various studies have shown that modifying the diet can significantly alter the plasma Ca and P values. The purpose of this study was to investigate the relationship between diet and plasma Ca and P levels and to potentially improve the Ca: P ratios of three Kemp's ridley sea turtles (Lepidochelys kempi) before their impending release.

Three healthy, juvenile sea turtles were fed strictly peeled, food quality shrimp for seven days. On day eight, the diet was changed to strictly bait shrimp with shells and heads for another consecutive seven days. Their previous diet, during rehabilitation from cold stunning, consisted of capelin, squid and small amounts of shrimp with no additional supplementation. Pre-trial and trial diets were formulated, based on nutritional analyses available on packaging and from previously analyzed samples. All turtles were eating between 2.2 and 2.9% of body weight (BW) in food daily comprising 23-30 kcal/kg/day.

From the time of presentation at Mote Marine Laboratory to the time of the first blood collection for the study eight months later, all three turtles had Ca: P < 1. Blood was taken on days 1, 3, 7, 10, 14 and 17 of the trial. Samples were collected from an external jugular vein, and chemistries were processed at an outside laboratory on a Hitachi blood chemistry analyzer.

The Ca: P ratio was found to further decline within the first three days of feeding exclusively peeled shrimp. The ratio increased within the first three days of feeding exclusively bait shrimp with heads and shells and normalized above one after only seven days on the whole shrimp diet. Turtles showed no abnormal clinical signs prior to the trial. The turtle with the lowest Ca: P ratio on day seven showed mild lethargy and had a decreased appetite, which improved with the dietary change to shrimp with shells. All three continued to gain weight and remained healthy. They were released off of Cape Canaveral, Florida a short time later. Laboratory analysis revealed that on an as-fed basis, shrimp with shells and heads had 16.5 times more Ca and half of the P by weight than peeled shrimp. This study provided preliminary evidence of the relationship between plasma Ca and P levels and diet in Kemp's ridley sea turtles as well as suggesting that feeding shrimp with shells as opposed to peeled shrimp is more appropriate in the sea turtle diet.