Di-(2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer and a pervasive environmental contaminant known to exert harmful effects on various animal species. While it is known to disrupt female reproduction in mammals, the effects on fish reproduction remain unclear. In this investigation, mature female koi carp (Cyprinus carpio) were exposed to nominal DEHP concentrations of 1, 10 and 100 µg/L for a period of 60 days to assess reproductive performance. The results revealed a marked decline in the gonadosomatic index (GSI) of females exposed to 10 and 100 µg/L DEHP. Histopathological examinations of ovarian tissues demonstrated severe structural damage, including oocyte atresia, intra-oocyte vacuolization and necrotic changes. Fecundity and oocyte diameter were significantly reduced in the same exposure groups. Biochemical analyses of ovarian fluid indicated notable alterations in glucose, cholesterol and total protein levels, while ionic concentrations of sodium, potassium, calcium and magnesium also showed significant variations among treated fish. Moreover, serum hormone assays demonstrated decreased levels of 17β-estradiol and elevated concentrations of 11-ketotestosterone in DEHP-exposed females. Gene expression analysis using real-time PCR revealed concentration-dependent changes in the transcription levels of key reproductive genes, including Fshr, Lhr, Ar, Erα and Erβ. When DEHP-exposed females were bred with unexposed males, substantial declines in fertilization, hatching and larval survival rates were observed. In summary, this study provides compelling evidence that chronic exposure to environmentally relevant concentrations of DEHP can impair reproductive physiology, disrupt endocrine function and diminish overall reproductive success in female koi carp.
Keywords: DEHP, Cyprinus carpio, reproductive toxicity, breeding performances