Effects of Dietary Soy Protein Concentrate on Growth, Digestive Enzymes Activities and Target of Rapamycin Signaling Pathway Regulation in Juvenile Soft-Shelled Turtle, Pelodiscus sinensis

Abstract

Soft-shelled turtle, Pelodiscus sinensis is important aquatic species in China, and searching for alternatives protein resources\rto fish meal (FM)-based feeds in feed has become urgent and important for its sustainability\rdevelopment. The present study was conducted to assess the effects of dietary soy\rprotein concentrate (SPC) on growth, digestive enzymes and target of rapamycin (TOR)\rsignaling pathway of juvenile P. sinensis (4.56 ± 0.09 g). SPC was applied to replace FM protein at 0%, 15%, 30% and 60% (designated\ras T0, T15, T30 and T60, respectively), and each diet was fed to triplicate groups.\rThe results showed that there was no significant difference in growth performance\rand feed utilization except of the turtles fed with T60 diet, of which showed poorer\rdaily weight gain and feed conversion rate. The pepsin/trypsin and Na+-K+ ATP-ase activities decreased dramatically when SPC level increased, and lipase activities\rin liver and intestinal tract also showed decline tendency. However, amylase activities\rwere unaffected. No significant differences were observed in TOR, S6K1 and 4E-BP1\rgenes mRNA expression level of TOR signaling pathway among the treatments. However,\rthe relative phosphorylated level of these proteins decreased significantly when SPC level increased. The present\rstudy indicated that high SPC substitution level would suppress digestive\renzymes and TOR signaling pathway proteins phosphorylated level and eventually result\rin growth reduction of P. sinensis.