Heat stress is a major environmental stressor that affects fish metabolism, growth, and death rates. This research examined the impact of dietary rutin addition (0, 100, 300, or 500 mg/kg) for 60 days on juvenile hybrid fish (Carassius auratus cuvieri, WCC, ♀ × Carassius auratus red var, RCC, ♂, WR) (27.97 ± 0.56 g) under heat stress conditions (32 ± 1 °C for 48 h). The analysis focused on blood parameters, oxidative stress biomarkers, and hepatic hsp70 and hsp90 gene expression in WR. The results demonstrated that rutin supplementation elevated blood glucose levels and the liver activities of glutathione reductase, glutathione peroxidase, catalase, and total superoxide dismutase in comparison to the control group. Additionally, rutin supplementation also significantly reduced serum cortisol and hepatic malondialdehyde levels while upregulating hepatic hsp70 and hsp90 gene expression. These findings suggest that rutin supplementation enhances antioxidant responses and alleviates the impact of heat stress on fish physiological and biochemical markers and heat shock protein gene expression.

Nonylphenol (NP) is a known endocrine-disrupting chemical (EDC) that has been shown to affect bone development in mammals. However, the detrimental impacts of NP on the skeletal growth and development of aquatic species, especially bony fish, remain poorly understood. Bone morphogenic proteins (BMPs), essential for bone formation and osteoblast differentiation, act through the BMP-Smad signaling pathway. In this study, two BMP genes, BMP2 and BMP4, were cloned and characterized in the red crucian carp (Carassius auratus red var.). The full-length cDNAs of BMP2 and BMP4 were 2029 bp and 2095 bp, respectively, encoding polypeptides of 411 and 433 amino acids, and share a typical TGF-β domain with other BMPs. The tissue expression patterns of both genes were identified, showing ubiquitous expression across all studied tissues. Additionally, the exposure of embryos or adult fish to NP stress resulted in a downregulation of BMP2, BMP4, and other genes associated with the BMP-Smad signaling pathway. Moreover, the combined treatment of adult fish with NP and the specific BMP receptor inhibitor significantly reduced these genes’ expression. These findings elucidate the mechanism of NP stress on BMP2 and BMP4, suggesting a role for the BMP-Smad signaling pathway in the response to endocrine-disrupting chemicals in fish.