Novel nutritional strategy: Dietary valine improves the health value and nutrient deposition in grass carp (Ctenopharyngodon idella)

Abstract

Grass carp (Ctenopharyngodon idella) is one of the most economically valuable freshwater fish in China, which is popular among consumers since its high-quality protein and low price. Valine is an essential amino acid for fish. In this study, dietary valine was assessed for the growth performance, muscle nutrient deposition, health value, and sensory quality of sub-adult grass carp. Over 10 weeks, 450 grass carp (539.8 ± 0.89 g) were fed six diets with varying levels of valine (2.8, 6.0, 9.0, 12.4, 16.2 and 19.4 g/kg diet). Results showed that appropriate dietary valine level (9.0 g/kg diet) increased percent weight gain (PWG), feed efficiency (FE) and specific growth rate (SGR), promoting the growth of grass carp. Appropriate dietary valine level improved shear force, pH_0h, and decreased cooking loss and lactate content, improving the sensory quality in the muscle of grass carp. Appropriate dietary valine level improved the muscle contents of crude protein and protein-bound amino acids, might be associated with the up-regulating of IGF-1/PI3K/AKT/TOR/S6K1/4EBP1 signaling pathway and down-regulating the ubiquitin lysosomal pathway. Appropriate dietary valine level increased the muscle contents of crude lipid and unsaturated fatty acids (UFAs), which partly be related to the reason that valine: (1) up-regulating the sterol regulatory element binding protein 1 (SREBP1) signaling pathway to enhance fatty acid synthesis; (2) down-regulating the peroxisome proliferator-activated receptor alpha (PPARα) pathway to inhibit fatty acid decomposition. In summary, dietary valine enhanced the growth performance, muscle nutrients deposition, health value and sensory quality in sub-adult grass carp, which have important guiding significance for the regulation of flesh quality and nutritional studies in fish. According to the broken-line regression analysis, the dietary valine requirement of sub-adult grass carp was 8.96 g/kg diet (34.30 g/kg protein) based on PWG.