This review paper presents fish reproductive toxicology studies with a specific focus on endocrine-disrupting chemicals (EDCs) present in the aquatic environment. These substances, including bisphenols, heavy metals, pesticides, phthalates, and polychlorinated biphenyls (PCBs), act as hormone mimics, receptor blockers, or enzyme inhibitors that affect hormonal regulation in the hypothalamic-pituitary-gonadal (HPG) axis. In this review, we provide an overview of the adverse effects of these pollutants on both female and male fish reproduction (i.e., hormonal disruption in the HPG axis, gametogenesis disorders, disturbed embryogenesis, etc.). Even at low concentrations, EDCs can exhibit reproductive toxicity in fishes. They can affect the functioning of certain systems within the hypothalamus (Kiss/GPR54, GnRH) and can also impact luteinizing hormone (LH) secretion in the pituitary. These compounds have negative impacts on gonads, oocyte maturation, steroidogenesis, and gametes. Early-life exposure to these substances not only affects embryonic development, resulting in increased mortality and body malformations, but this also induces genetic changes in newly hatched larvae. All these observations underscore the need for monitoring the aquatic environment for EDCs and implementing protective measures to preserve the health and welfare of fishes and safeguard water ecosystems.

Recent studies have clearly shown that vitamin D₃ is a crucial regulator of the female reproductive process in humans and animals. Knowledge of the expression of vitamin D₃ receptors and related molecules in the female reproductive organs such as ovaries, uterus, oviduct, or placenta under physiological and pathological conditions highlights its contribution to the proper function of the reproductive system in females. Furthermore, vitamin D₃ deficiency leads to serious reproductive disturbances and pathologies including ovarian cysts. Although the influence of vitamin D₃ on the reproductive processes of humans and rodents has been extensively described, the association between vitamin D₃ and female reproductive function in farm animals, birds, and fish has rarely been summarized. In this review, we provide an overview of the role of vitamin D₃ in the reproductive system of those animals, with special attention paid to the expression of vitamin D₃ receptors and its metabolic molecules. This updated information could be essential for better understanding animal physiology and overcoming the incidence of infertility, which is crucial for optimizing reproductive outcomes in female livestock.

In recent years, vitamin D₃ has been revealed as an important regulator of reproductive processes in humans and livestock; however, its role in the female reproductive system of poultry is poorly known. The aim of this study was to examine vitamin D₃ receptor (VDR and PDIA3) and metabolic enzyme (1α-hydroxylase and 24-hydroxylase) mRNA transcript and protein abundances, and protein localization within the hen ovary, oviductal shell gland, pituitary, liver, and kidney. We demonstrated, for the first time, the patterns of the relative mRNA and protein abundances of examined molecules in the ovary, dependent on follicle development and the layer of follicle wall, as well as in other examined organs. Immunohistochemically, PDIA3, 1α-hydroxylase, and 24-hydroxylase are localized in follicular theca and granulosa layers, luminal epithelium and tubular glands of the shell gland, pituitary, liver, and kidney. These results indicate that reproductive tissues have both receptors, VDR, primarily involved in genomic action, and PDIA3, probably participating in the rapid, non-genomic effect of vitamin D₃. The finding of 1α-hydroxylase and 24-hydroxylase expression indicates that the reproductive system of chickens has the potential for vitamin D₃ synthesis and inactivation, and may suggest that locally produced vitamin D₃ can be considered as a significant factor in the orchestration of ovarian and shell gland function in hens. These results provide a new insight into the potential mechanisms of vitamin D₃ action and metabolism in the chicken ovary and oviduct.

The aim of this study was to investigate the bioaccumulation of cadmium in the muscle tissue of Prussian carp during 7 and 13 weeks of exposure to different concentrations of this metal in water (0.4 and 4.0 mg/L), and the depuration of cadmium from muscle during the following 6-week depuration period in the presence of melatonin implants. Furthermore, the relationship between cadmium accumulation and the levels of essential bioelements (copper, zinc, iron) in muscle was evaluated, as well as the bioconcentration factor of cadmium. Heavy metal concentration was determined using atomic absorption spectrometry. Cadmium accumulation in fish muscle increased with the duration of exposure. Cd concentrations exceeded the permissible levels for human consumption in groups exposed to the higher concentration of this metal. Moreover, a significant increase of Zn and Fe levels in the muscle was observed. In the fish that received melatonin implants and were exposed to Cd, its level in the muscle was significantly lower. The depuration of accumulated cadmium depended mainly on the duration of the elimination period. This is the first study to report that melatonin co-administration can effectively protect the fish from the accumulation of cadmium in muscle tissue and changes in trace metal levels.