Effects Of Dietary Riboflavin On Gill Immune Function And Flesh Quality Of Young Grass Carp (Ctenopharyngodon Idella) And The Mechanisms

Riboflavin is an essential vitamin for fish. Studies have indicated that riboflavin could improve the growth performance of fish. However, few reports focused on the effect of riboflavin on gill health and flesh quality of fish. This study investigated the effects of riboflavin on growth, gill health, flesh quality and related signaling molecules of young grass carp(Ctenopharyngodon idella). The riboflavin requirements for young grass carp, based on different indicators, were also determined in this study. In this study,540 healthy fish (mean weight 275.82 ± 0.57 g) were randomly distributed into 18 experimental cages, and the 18 experimental cages were randomly distributed into 6 groups. Each group was fed the diets containing riboflavin at 0.63 (control),1.95,3.98, 6.02,7.96 and 10.04 mg/kg diet for 8 weeks.Study showed that optimum dietary riboflavin improved the percent weight gain (PWG), specific growth rate (SGR), feed intake (FI) and feed efficiency (FE) (P< 0.05). Meanwhile, optimum dietary riboflavin increased lysozyme (LA) and acid phosphatase activities, complement component 3 content (P< 0.05). Moreover, mRNA levels of interleukin 10 (IL-10), transforming growth factor β1 (TGF-β1), inhibitor of κBα (IκBα) and target of rapamycin (FOR) were increased (P< 0.05), while, the mRNA levels of interleukin 1β (IL-1β), interleukin 8 (IL-8), interferon γ2 (IFN-γ2), tumor necrosis factor α (TNF-α), nuclear factor kappa B p65 (NF-κB p65), IκB kinase β (IKKβ) and IκB kinase y (IKKγ) were decreased (P< 0.05). However, dietary riboflavin has no impact on IκB kinase α(IKKα) mRNA level(P> 0.05). Optimal dietary riboflavin increased Claudin-3, Claudin-c, Occludin and ZO-1 mRNA levels (P< 0.05), and decreased Claudin-12 and myosin light chain kinase (MLCK) mRNA levels (P< 0.05). However, dietary riboflavin has no impact on Claud in-b and Claudin-15a mRNA levels (P> 0.05).The effects of riboflavin on flesh quality were listed as follows. Optimal riboflavin increased protein. pH, shear force, glutamic acid, leucine, hydroxyproline, lipid and proline (P< 0.05); and decreased moisture, lactate content and cooking loss (P< 0.05). Furthermore, optimal riboflavin reduced ROS production, decreased malondialdehyde (MDA) and protein carbonyl (PC) contents (P< 0.05), increased activities of copper/zinc superoxide dismutase (CuZnSOD). catalase (CAT). glutathione peroxidase (GPx). glutathione reductase (GR). anti-superoxide anion (ASA) and anti-hydroxy radical (AHR) and glutathione (GSH) content (P< 0.05); increased CuZnSOD. GR. CAT, GPx and nuclear factor erythroid-2 related factor 2 (Nrf2) mRNA levels (P< 0.05); decreased Kelch-like-ECH-associated protein 1b (Keap1b) mRNA level in the muscle (P< 0.05). However, dietary riboflavin has no impact on Keapla mRNA level in the muscle (P> 0.05).In conclusion, optimal riboflavin improved growth, gill immunity and physical barrier function, flesh quality and regulated the mRNA expression of related signaling molecules. Based on PWG and LA activity in the gill, the riboflavin requirements for young grass carp (275-722 g) were 5.85 and 7.39 mg/kg diet, respectively.