Effects of dietary vitamin C on growth, lipid oxidation, and carapace strength of soft-shelled turtle, Pelodiscus sinensis
Introduction
Ascorbic acid (vitamin C) is a strong metabolic reducing agent that is responsible for the absorption of iron in the animal body (Brise and Hallberg, 1962); antioxidation (Buettner and Jurkiewicz, 1996); formation of collagen (Myllyla et al., 1978); immunity (Hardie et al., 1991, Lim et al., 2001); metabolism of tryptophan, tyrosine, and cholesterol (Tolbert, 1985); as well as other physiological functions of animals. A deficiency of vitamin C results in bone or hard tissue deformation (Andrew and Murai, 1975, Lim et al., 2001).
The capacity to biosynthesize vitamin C originated in the kidney of amphibians, evolved in reptiles, and finally became a function of the liver of mammals. This capacity was lost within the guinea pig, the flying mammals, monkeys, and humans (Chatterjee, 1973). In addition, the ability to synthesize vitamin C is absent in the insects, invertebrates, and fishes.
The soft-shelled turtle Pelodiscus sinensis is a high-value aquaculture organism in Asian countries. Because it is a reptile, it should be able to produce sufficient vitamin C to support its own growth and physiological functions. A previous report has identified a dietary requirement of vitamin C for this species based on specific growth rate (Zhou et al., 2003). However, the dietary vitamin C level tested in that report was fairly high (0–10,000 mg/kg) as compared to other species. In the present study, we re-evaluated not only the growth but also the collagen content and strength of the carapace of the soft-shelled turtle to estimate the dietary vitamin C requirement using a regression model.
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Animals
Juvenile soft-shelled turtles (P. sinensis) were cultured in our laboratory. Fertilized turtle eggs were transferred to our laboratory from a turtle farm located at Pingtung, Taiwan. The eggs were incubated in our laboratory at 30 °C for approximately 45 days to produce juveniles. These juvenile turtles were then acclimated to laboratory conditions and fed on a vitamin C-free basal diet for 4 weeks. Culture conditions were similar to those described (Chen et al., 2014, Chen and Huang, 2011, Chu et
Growth and muscle composition
No mortality was observed during the entire feeding trial. No significant difference (p > 0.05) was observed on both growth performance and feed utilization among turtles fed different levels of vitamin C (Table 2). Furthermore, the muscle composition of the turtles was not affected by different dietary treatments (Table 3).
Hepatic vitamin C and lipid oxidation
Although the difference was not statistically significant due to high deviations within samples, the hepatic vitamin C concentration of the turtles fed the vitamin C-free diet
Discussion
It has been recognized that reptiles are able to biosynthesize vitamin C (Chatterjee, 1973). Vitamin C synthesis requires enzyme l-gulonolactone oxidase that catalyzes the final stage of vitamin C formation. During our preliminary qualitative analysis, we have also found the presence of this enzyme activity in soft-shelled turtles. Therefore, we did not think a dietary vitamin C requirement for growth of soft-shelled turtles existed before the trial. Furthermore, Chen et al. (2015) recently
Acknowledgment
This study was supported by a grant from the Ministry of Science and Technology, Taiwan under grant number NSC-102-2313-B-415-003.
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