Role of 17β-estradiol injection on growth, physiology, and reproductive performance in male goldfish (Carassius auratus) with or without female interaction.

This study investigated the effects of 17β-estradiol (E2) on male goldfish, with particular focus on how social interactions modify physiological responses. Four experimental groups were housed in 80 L tanks and received two injections at 14-day intervals over 28 days: MF (5 males + 5 females, sesame oil), M (10 males, sesame oil), MEF (5 males + 5 females, E2), and ME (10 males, E2). The MF group exhibited the highest growth performance, with significantly greater final weight (36.3 ± 1.1 g), weight gain (11.3 ± 1.4 g), and specific growth rate (1.8 ± 0.2% day⁻) (P < 0.05). E2 exposure disrupted biochemical parameters, elevating cholesterol and triglycerides while reducing glucose and phosphorus (P < 0.05). Testosterone levels were significantly lower in E2-treated groups, with MF maintaining the highest levels (P < 0.05). Sperm activity and motility were severely impaired in E2-treated groups, with MF showing the highest sperm activity (95.6%) and motility time (371.2 sec) (P < 0.05). Gonadosomatic index was highest in MF (5.99%) but significantly reduced in MEF (4.56%), indicating gonadal impairment (P < 0.05). E2 exposure and social isolation inhibited spermatogenesis, reducing spermatogonia and spermatocytes. Liver histopathology revealed severe damage in ME, while MF displayed optimal hepatic structure. These results highlight the negative impact of E2 exposure on growth, reproduction, and liver function, while social interactions mitigated some effects. This underscores the complex interplay between endocrine disruption, social dynamics, and physiological health in goldfish.