Effects of Dietary Paper Mulberry (Broussonetia papyrifera ) on Growth Performance and Muscle Quality of Grass Carp ( Ctenopharyngodon idella )

The present study investigated the effects of dietary paper mulberry ( , BP) on growth performance, muscle quality and muscle growth-related mRNA expressions of grass carp. Fish (initial weight: 50.0 ± 0.5 g) were fed diets supplemented with 0% (control diet), 5%, 10%, 15% and 20% BP for 8 weeks. The results showed that increasing levels of paper mulberry linearly and quadratically decreased the special gain rate (SGR) and increased the feed conversion rate (FCR) of grass carp ( 0.05). Significantly positive quadratic trends were found between paper mulberry levels and muscle crude fat or crude protein of grass carp ( 0.05). In comparison to the control diet, the 10%BP and 15%BP groups had significantly decreased muscle crude fat and increased crude protein ( 0.05). The levels of paper mulberry resulted in a linear and quadratic increase in water loss of grass carp muscle ( 0.05), and all groups with paper mulberry supplementation were significantly higher than the control group ( 0.05). Significant positive linear and quadratic trends were found between the paper mulberry levels and muscle fiber diameter or density of grass carp ( 0.05). In comparison to the control diet, the significant differences were found in the 15%BP and 20%BP groups ( 0.05). The muscle adhesiveness and hardness linearly and quadratically increased with the increasing levels of paper mulberry ( 0.05), and both of which increased significantly when the level of paper mulberry reached 10% ( 0.05). In addition, the increase in paper mulberry linearly and quadratically improved the expressions of myoblast determination protein (MyoD), myogenin (MyoG), paired box protein 7 (Pax7) and myostatin 1 (MSTN1) ( 0.05). When the supplementation of paper mulberry reached 15%, the expressions of all these mRNAs were significantly higher than those of the control group ( 0.05). In summary, adding 5% paper mulberry did not affect the growth of grass carp. However, the supplementation of 10% paper mulberry could improve muscle quality through improving muscle hardness, reducing fat accumulation and muscle fiber diameter, at the cost of reducing growth performance.