Differential effects of dietary Zn deficiency and excess on carnitine status, kinetics and expression of CPT I in yellow catfish Pelteobagrus fulvidraco

• Zn deficiency and excess differentially affect carnitine composition in fish.
• Differential effect on CPT I kinetics is found in fish exposed to dietborne Zn.
• Zn differentially affects the mRNA levels of four CPT I isoforms in fish.
• Zn changes CPT I kinetics via altering its expression and carnitine status.

The present study was conducted to determine the effect of dietary Zn deficiency and excess on carnitine status, kinetics and expression of CPT I in the liver and muscle of yellow catfish Pelteobagrus fulvidraco. Yellow catfish were subjected to 20 (adequate Zn), 11.45 (Zn deficiency) and 155 (Zn excess) mg kg− 1 diet for 8 weeks. In the liver, Zn deficiency increased FC, AC and TC contents and did not significantly affect the ratios of FC/TC and AC/FC. Similarly, Zn excess also increased TC and AC contents, and AC/FC ratios, but reduced FC content and FC/TC ratio. In the muscle, FC content was promoted by Zn deficiency and inhibited by Zn excess. FC/TC ratio was stimulated by Zn deficiency and inhibited by Zn excess. In contrast, AC/FC ratio was reduced by Zn deficiency and induced by Zn excess. Zn deficiency also reduced Km and Vmax values while Zn excess increased them in the liver and muscle. Zn deficiency and excess influenced the expression levels of four CPT I isoforms, such as CPT Iα1b, CPT Iβ, CPT Iα2a and CPT Iα1a in the liver and muscle. Furthermore, some correlations were observed in between the expression levels of CPT I isoforms and Km for carnitine, and between CPT I isoform expression and CPT I activity. Thus, for the first time, our study indicated that Zn deficiency and excess showed differential effects on carnitine status, kinetics and expression of CPT I in yellow catfish, which helped provide some novel insights into Zn nutrition and toxicology in fish.