DIFFERENT DIETARY ZINC SOURCES ON MUSCLE ZINC TRANSPORT AND DEVELOPMENT OF JUVENILE GRASS CARP (CTENOPHARYNGODON IDELLA)

In this study, juvenile grass carp (Ctenopharyngodon idella) was utilized as the object to explore the effect of different dietary zinc sources on muscle zinc transport and development. Five experimental diets were formulated, including a reference diet without any added zinc sources (Control), a diet supplemented with Zn sulfate (ZnSO₄), Zn dioxide nanoparticles (ZnO NPs), Zn lactate (Zn-Lac), and Zn glycine chelate (Zn-Gly), respectively. Grass carp with an initial body weight of 3.54 g/fish were fed one of these five experimental diets for 8 weeks. The myofiber diameters of grass carp fed diets containing the four zinc sources showed increases compared to those in reference diet group, with the Zn-Gly group exhibiting the highest frequency of myofibers with diameter >50 μm. The mRNA expression levels of Zn transport-related genes significantly changed in all experimental groups (ZnSO₄, ZnO NPs, Zn-Lac, and Zn-Gly), compared to the reference diet group, particularly in the Zn sulfate group (P<0.05). Furthermore, the addition of the four zinc sources up-regulated the mRNA abundance of muscle development-relevant genes (mef2d, myog, and myod) compared to the reference diet group (P<0.05). Notably, the myod mRNA level was significantly higher in the Zn-Gly group than those in the other three dietary groups (ZnSO₄, ZnO NPs, and Zn-Lac) (P<0.05). Moreover, the mRNA expression levels of map3k2, map2k7, and jnk genes were significantly higher in grass carp fed with ZnSO₄, ZnO NPs, Zn-Lac, and Zn-Gly groups than those in the reference diet group (P<0.05). Importantly, the mRNA expression level of map2k7 was significantly up-regulated in the Zn-Gly group than those in the ZnSO₄, ZnO NPs, and Zn-Lac groups (P<0.05). This study suggests that Zn-Gly is beneficial for muscle development and that the MAPK/JNK signaling pathway potentially mediates this crucial biological process. The present study provide the good basis for further understanding into the effect of Zn-Gly on muscle development in fish and offer implications for its application in the aquafeeds.