Seasonal Dynamics of Testosterone and Reproductive Physiology in Amur Common Carp (Cyprinus carpio haematopterus)

Abstract

The steroid hormone testosterone plays a central role in the reproductive physiology of fish, regulating gamete maturation, spermatogenesis, secondary sexual characteristics, and spawning. Although seasonal variations in sex steroids have been documented in several fish species, information on the Amur common carp (Cyprinus carpio haematopterus), an economically important species in freshwater aquaculture, remains limited. The present study investigated seasonal fluctuations in testosterone levels in the plasma and gonadal tissues of Amur carp broodstock of two age groups (1+ and 2+ years old) reared under pond culture conditions. Blood and gonadal samples were collected across the four seasons, and testosterone concentrations were quantified using reverse-phase high-performance liquid chromatography (RP-HPLC). Water quality parameters were monitored regularly, and the data were statistically analyzed using one-way ANOVA. The results revealed a distinct seasonal pattern in both age groups, with testosterone concentrations peaking in spring and reaching their lowest levels in autumn. Testosterone was also evident in females with males exhibiting consistently higher concentrations (ng/mg) (3.70±0.02; 4.20±0.06) than females (2.85±0.08; 2.40±0.03) for gonad and plasma respectively. The presence of testosterone in females supports its role as a precursor of estrogen biosynthesis.  The observed hormonal changes were closely correlated with gonadosomatic index (GSI) values and seasonal change in environmental water conditions. Furthermore, older brood stock (2+ years old) demonstrated stronger hormonal responses and reproductive potential than younger fish (1+ year). These findings highlight spring as the optimal season for breeding and brood stock management of Amur carp and provide valuable insights for improving early breeding and seed production strategies in freshwater aquaculture.