Evaluating sperm characteristics from stripping and testicular extraction in northern pike (Esox lucius) with a focus on stability during storage.

The quality and quantity of stripped and testicular wild northern pike (Esox lucius) sperm was compared and the effectiveness of short-term storage was assessed. Stripped sperm (SS) was collected using abdominal massage. Next, the fish were decapitated and the testes were removed. Testicular sperm (TS) was collected by gently macerating the testes through double-layered gauze. The volume and number of sperm were assessed in SS and TS. Computer-assisted sperm analysis (CASA) was used to determine SS and TS motility and kinetic parameters. Undiluted samples of SS and TS were then stored short-term under refrigeration (8°C) for 72 h. A higher volume and number of sperm were noted for TS compared to SS. On the other hand, motility and kinetic parameters of SS and TS were similar immediately after collection. Seminal plasma osmotic pressure was lower in SS compared to TS. Regardless of the sperm source (SS or TS), values of sperm motility and kinetic parameters remained high during short-term storage for 24 h. However, after 48 and 72 h significant decreases in the values of MOT, curvilinear velocity (VCL, μm s-1), straight-linear velocity (VSL, µm s-1), and amplitude of lateral head displacement (ALH, µm) parameters were noted in SS compared to TS. This indicated that northern pike sperm obtained from spermatic ducts lost their biological value (fertilization capacity) much faster than that obtained from testes. This was most likely due to the presence of urine and its long-term negative impact on storage efficiency of SS compared to TS.