Evaluation of the protein requirement of juvenile Chinese soft-shelled turtle (Pelodiscus sinensis, Wiegmann) fed with practical diets

• Growth of Chinese soft-shelled turtles increased as dietary protein increased up to 33% followed by a plateau stage from 33% to 43%.
• Protein efficiency ratio and protein productive value were highest in soft-shelled turtles fed with 33% protein diet.
• Body lipid of soft-shelled turtles decreased with increasing dietary protein level.
• The estimated dietary protein requirement using specific growth rate (SGR) as the indicator is 32.8% for soft-shelled turtles.

A feeding trial was conducted to determine the optimal protein requirement of juvenile Chinese soft-shelled turtle (Pelodiscus sinensis). Seven isoenergetic diets containing graded levels of protein (25%, 27%, 29%, 31%, 33%, 35%, and 43%) were fed to turtles initially averaging 4.8 ± 0.7 g for 8 weeks. The specific growth rate (SGR) of turtles increased significantly with dietary protein from 25% to 33% without any further significant increases in SGR at 35% or 43% protein. Feed intake was highest in turtles fed with the diet containing 25% protein, followed by the 27–31% protein groups, and was lowest in turtles fed with the 33–43% protein diets. Feed efficiency (FE) of turtles followed an inverse pattern with feed intake. Protein efficiency ratio (PER) in turtles initially increased with dietary protein levels, with the highest value observed in the 33% protein group, followed by decreases with further increases in dietary protein content. Protein productive value (PPV) of turtles followed the same pattern as PER. Body lipid content decreased with increasing dietary protein level. Analysis of SGR by broken-line regression indicated that the estimated optimal dietary level of protein for juvenile Chinese soft-shelled turtles was 32.8%.