Intestinal Accumulation of Polyester Microfibers Modulates HPG Axis Regulation and Oocyte Maturation in Zebrafish (Danio rerio)

Polyester microfibers (MF) are widespread in aquatic environments and increasingly recognized as an emerging factor affecting fish physiology. This study aimed to investigate the effects of intestinal accumulation of MF on gut tissue and cellular alterations, as well as on the HPG axis and oocyte maturation in adult female zebrafish. Adult female zebrafish were exposed to environmentally relevant concentrations of MF (1000 and 3000 particles/L) for 14 days to examine endocrine-regulated physiological and reproductive responses. For comparative reference, a bisphenol A (BPA) exposure group was included to contextualize endocrine-related responses. MF exposure resulted in intestinal accumulation. Gene expression analyses showed increased expression of vtg1 and esr2a, along with decreased expression of gnrh3, fshβ, lhβ, cyp17, and cyp19a1, indicating altered regulation of the HPG axis and steroidogenic pathways. Ovarian histology revealed alterations in oocyte development, especially at the higher MF concentration, indicating that MF can affect endocrine-regulated physiology and reproduction in fish. Together, these findings provide new evidence that intestinal accumulation of microfibers, along with associated histological and transcriptional alterations, elicits estrogen-responsive physiological patterns that influence HPG axis regulation and oocyte maturation in fish.