Reproductive effects of chronic dietary exposure to arsenic-contaminated oligochaetes in Zebrafish (Danio rerio)

The reproductive consequences of environmentally relevant trophic exposure to arsenic in fish are poorly understood, despite diet being the major exposure source in many contaminated systems. This study investigated the reproductive effects of chronic dietary exposure to arsenic in adult Zebrafish via arsenic-contaminated oligochaete (Lumbriculus variegatus) worms. Worms pre-exposed to arsenite (0, 2.5, and 5.0 mg/L) for 14 days resulted in arsenic body burdens of 0.25 (Control), 34.69 (Low), and 77.79 (High) μg/g dry weight. Zebrafish were fed these worms at 3.5 % of body weight twice daily for 60 days. Reproductive endpoints assessed included gonadosomatic index (GSI), hepatosomatic index (HSI), fecundity, fertilization rate, and mating behaviour. Brain, liver, gonads, and blood plasma were assessed for gene expressions related to hypothalamus-pituitary-gonadal (HPG) axis genes, oxidative damage in hepatic and gonadal tissues, and to quantify the circulating 17β-estradiol (E2), 11-keto testosterone (11KT), and vitellogenin (VTG) levels in males and females. Sperm density and motility were assessed in males, and gonadal histopathology was conducted in both sexes. Dose-dependent reductions in GSI, HSI, fecundity, fertilization rate, and mating behaviour were recorded, along with oxidative damage in gonadal and liver tissues. Arsenic also reduced sperm quality and decreased the proportion of mature gametes in both ovaries and testes. Chronic exposure significantly altered HPG axis gene expression and disrupted circulating E2, 11-KT, and VTG levels in both sexes. Overall, these findings provide novel mechanistic insights into arsenic-induced reproductive toxicity in fish, which have important implications for understanding the consequences of arsenic contamination in aquatic ecosystems.