Detalle de: Species-specific responses of fish sperm to thermal incubation and activation during short-term storage

Although short-term storage of diluted sperm at 0–2 °C with extenders has been shown to effectively preserve sperm quality, its broad applicability across fish species with different thermal preferences—and the ability of stored sperm to respond to elevated incubation or activation temperatures—remains insufficiently understood. To investigate this further, sperm samples from six species: zebrafish, common carp, European eel, gilthead seabream, sterlet and rainbow trout, were accordingly diluted with immobilising solutions and stored at 0–2 °C under aerobic conditions for 1 to 28 days depending on the species. The effect of the following incubation and activation at low (4 °C) and relatively high temperatures (natural species-specific spawning temperature) on various spermatozoa motility parameters during the storage was estimated. During sperm storage, sperm motility and velocity declined when activated at the species-specific spawning temperature. Nevertheless, incubation and activation at higher temperatures were associated with improved motility parameters in several species. Significant variations were observed between different species in spermatozoa motility (MOT) and velocity (VCL and VSL) during storage, particularly in response to low- or high-temperature incubation and activation. PCA of stored spermatozoa revealed distinct clustering of motility parameters in zebrafish, common carp, and sterlet, indicating clear thermal response patterns. In contrast, European eel and gilthead seabream exhibited no such clustering, reflecting interspecific variability in thermal sensitivity. GLMM analysis revealed that sperm motility parameters were generally affected, albeit to varying degrees, by thermal conditions during incubation and activation. Further validation using an XGBoost model revealed that storage duration, incubation, and activation temperatures markedly impacted sperm motility in thermophilic and mesophilic fish species (zebrafish, common carp, and European eel) compared to the other species. These results underscore the broad applicability and effectiveness of chilled sperm storage at 0–2 °C for preserving sperm quality across diverse fish species under variable thermal incubation and activation conditions.