This exploratory study investigated associations between dietary algae supplementation (1% and 3%) and sperm quality in male common carp (Cyprinus carpio) broodstock during two consecutive spawning seasons under commercial farming conditions. Sperm quality was evaluated using conventional motility and kinetic parameters together with analyses of seminal plasma ion composition, glucose concentration, osmolality and fatty acid profiles. The data were evaluated across sampling periods characterised by different water temperatures relevant to broodstock management. Differences between control and algae-supplemented fish were observed in several reproductive parameters; however, these responses were not consistent across temperatures or spawning seasons. During the first spawning season, only limited differences between dietary groups were detected, whereas during the second season the algae-supplemented group exhibited higher sperm volume and total sperm number at 20.5°C. Seminal plasma osmolality differed between dietary groups across the tested sampling periods, whereas additional differences were observed in pH, ion concentrations and fatty acid composition. Variation among sampling periods characterised by different water temperatures was also observed for several sperm quality traits, including sperm density, motility, kinetic characteristics and seminal plasma ion and fatty acid profiles. Several parameters reached their highest values at intermediate sampling temperatures. Because the study was conducted under commercial farming conditions without pond-level replication, and because water temperature and reproductive maturation progressed simultaneously during the spawning season, the observed differences should be interpreted as preliminary associations rather than evidence of causal treatment effects. Overall, the findings suggest that dietary algae supplementation, particularly at the 3% inclusion level, may be associated with variation in selected sperm quality characteristics and seminal plasma composition under specific environmental conditions. However, further replicated and controlled studies are required to distinguish the effects of dietary supplementation, water temperature and reproductive maturation before definitive conclusions can be drawn.