Different effect of dietborne and waterborne Zn exposure on lipid deposition and metabolism in juvenile yellow catfish Pelteobagrus fulvidraco

Juvenile yellow catfish Pelteobagrus fulvidraco were exposed to 0.04 or 0.35 mg l−1 waterborne Zn, 27.25 or 213.84 mg kg−1 dietary Zn, singly or in combination for 42 days. Growth and lipid metabolism in juvenile yellow catfish were investigated. Growth and survival were significantly inhibited by single waterborne Zn exposure but not by dietary Zn exposure. Dietary Zn addition reduced but waterborne Zn exposure increased hepatic lipid content. In contrast, muscle lipid content was reduced by waterborne Zn exposure but not by dietborne Zn exposure. The single exposure also affected several lipogenic enzymatic activities and expression of genes (in this article gene expression is taken synonymous to mRNA expression) related to lipogenesis and lipolysis. Pearson correlations among lipid content, enzymatic activities and mRNA expression levels were also observed, suggesting that changes at molecular and enzymatic levels may underlie the patterns of lipid metabolism and accordingly affect lipid deposition. For the first time, our study demonstrates the differential effect of different Zn exposure pathways on lipid metabolism at the molecular level in fish, indicating that the exposure route is critical to lipid deposition and metabolism.