Dietary protein levels changed the hardness of muscle by acting on muscle fiber growth and the metabolism of collagen in sub-adult grass carp (Ctenopharyngodon idella)

Abstract

Background Nutrient regulation has been proven to be an effective way to improve the flesh quality in fish. As a necessary nutrient for fish growth, protein accounts for the highest proportion in the fish diet and is expensive. Although our team found that the effect of protein on the muscle hardness of grass carp was probably related to an increased collagen content, the mechanism for this effect has not been deeply explored. Moreover, few studies have explored the protein requirements of sub-adult grass crap (Ctenopharyngodon idella). Therefore, the effects of different dietary protein levels on the growth performance, nutritional value, muscle hardness, muscle fiber growth, collagen metabolism and related molecule expression in grass carp were investigated. Methods A total of 450 healthy grass carp (721.16 ± 1.98 g) were selected and assigned randomly to six experimental groups with three replicates each (n = 25/replicate), and were fed six diets with 15.91%, 19.39%, 22.10%, 25.59%, 28.53% and 31.42% protein for 60 d. Results Appropriate levels of dietary protein increased the feed intake, percentage weight gain, specific growth rate, body composition, unsaturated fatty acid content in muscle, partial free amino acid content in muscle, and muscle hardness of grass carp. These protein levels also increased the muscle fiber density, the frequency of new muscle fibers, the contents of collagen and IGF-1, and the enzyme activities of prolyl 4-hydroxylases and lysyloxidase, and decreased the activity of matrix metalloproteinase-2. At the molecular level, the optimal dietary protein increased collagen type I α1 (Colα1), Colα2, PI3K, Akt, S6K1, La ribonucleoprotein domain family member 6a (LARP6a), TGF-β1, Smad2, Smad4, Smad3, tissue inhibitor of metalloproteinase-2, MyoD, Myf5, MyoG and MyHC relative mRNA levels. The levels of the myostatin-1 and myostatin-2 genes were downregulated, and the protein expression levels of p-Smad2, Smad2, Smad4, p-Akt, Akt, LARP6 and Smad3 were increased. Conclusions The appropriate levels of dietary protein promoted the growth of sub-adult grass carp and improved muscle hardness by promoting the growth of muscle fibers, improving collagen synthesis and depressing collagen degradation. In addition, the dietary protein requirements of sub-adult grass carp were 26.21% and 24.85% according to the quadratic regression analysis of growth performance (SGR) and the muscle hardness (collagen content), respectively.

Improvement of muscle quality in tilapia (Oreochromis niloticus) with dietary faba bean (Vicia faba L.)

“…Some studies have also highlighted that textural features have a substantial favorable association with the muscle fiber density (28,29). Both connections between the density of muscle fibers and muscle hardness showed a clear positive correlation (13,30). Tilapia muscle fiber density rose at appropriate levels of dietary faba bean, showing that these levels promoted muscle fiber growth and that the rise in density may be linked to hyperplasia.…”

“…Both internal and external elements, such as culture environment ( 5 , 8 ), food nutrition ( 10 , 11 ), and genetics ( 12 ) have an impact on the quality of fish muscle. Fish flesh quality can be improved through nutrient control, which has been shown to be beneficial ( 13 ). Fish muscle quality improvement defined as higher muscle hardness and crispiness by feeding faba bean ( Vicia faba L.), has gained increasing research interest ( 14–17 ).…”

The flesh texture of teleost fish: Characteristics and interventional strategies

“…Therefore, dietary protein levels and sources are expected to affect the flesh texture of farmed fish. Recent study on grass carp documented that appropriate levels (22%–26%) of dietary protein increased muscle hardness 63 . The authors attributed this observation to (1) the increases of new fibres and myofiber density regulated by MRFs; (2) the increased collagen content, owing to its elevated anabolism and attenuated catabolism, regulated by TGF‐β1/Smad signalling and related enzymes (LOX and prolyl 4‐hydroxylases, two key enzymes catalysing collagen modification).…”

Intervention of Dietary Protein Levels on Muscle Quality, Antioxidation, and Autophagy in the Muscles of Triploid Crucian Carp (Carassius carassius Triploid)

“…For example, the protein inclusion level has been found to affect the growth performance and flesh quality of the fish, as well as alter the antioxidant capacity of grass carp [1]. In grass carp, muscle hardness is influenced by the dietary protein level, which affects the growth of muscle fibers as well as the synthesis and degradation of collagen [2]. In kuruma shrimp, a low dietary protein level has been shown to slow down the growth rate, decrease the intestinal trypsin activity, and affect the hardness [3].…”