Estimation of dietary copper requirement of juvenile soft-shelled turtles, Pelodiscus sinensis

Juvenile soft-shelled turtles (Pelodiscus sinensis) were fed diets containing 10 levels (0.8, 3.0, 5.0, 7.8, 9.0, 10.9, 20.4, 41.8, 78.6, 158 mg/kg diet) of copper (Cu) for 16 weeks. Turtles fed 5.0 mg Cu/kg achieved the best growth performance and the highest hematological values among all dietary groups. Growth was reduced significantly when dietary copper exceeded 20 mg/kg. Using the broken-line model with growth and hematological parameters as the dependent variables, the dietary Cu requirement of soft-shelled turtle was estimated to be 4.4-4.8 mg Cu/kg diet. Copper, iron, zinc and selenium concentrations in turtle liver were found to be influenced by dietary Cu level. Thiobarbituric acid-reactive substances in liver tissue of turtles fed diets containing 78.6-158 mg Cu/kg were higher (P < 0.05) than those fed diets containing less copper. Furthermore, diets containing more than 20 mg Cu/kg significantly impaired growth and hematology of soft-shelled turtles, indicating the dietary Cu tolerance above the requirement may be as low as 4 fold (20 vs. 5 mg/kg). Based on the results of this study, a dietary Cu level of 4-5 mg/kg is recommended for soft-shelled turtles.