Identification of the major proteins present in the seminal plasma of European eel, and how hormonal treatment affects their evolution. Correlation with sperm quality

• For the first time the 2DE protein composition of the seminal plasma of the European eel has been identified.
• Lipid transport proteins (apolipoproteins) could play a role in the early phases of sperm production.
• Immune system proteins (Complement C3) could have an immunologic role in the final stages of sperm maturation.
• It seems that proteins located at 19 KDa could be involved in the sperm motility of the European eel.

By first time, 2DE protein profile of European eel seminal plasma has been determined. 14 different proteins corresponding to 9 major families were identified in seminal plasma, through hormonal treatment. Some of them play a part in sperm maturation, including carbonic anhydrase which is responsible for modulating the pH of seminal plasma, and warm temperature acclimation protein, which may play an important role in the final maturation of this species, due to the warm temperature of their spawning ground (in the Sargasso Sea).Sperm samples were classified into three motility categories depending on the percentage of motile cells, I: 0–25%, II: 25–50% and III: > 50%. Different protein profiles were observed depending on the sperm motility categories, specifically, with the apolipoproteins and complement C3. Higher numbers of proteins from the apolipoprotein family were registered at lower motilities; whereas the complement C3-like family was higher in the samples with the highest percentage of motile cells. These results suggest that the proteins linked to the transportation of lipids (apolipoprotein) and to the immune system (complement C3) may carry out their functions at different stages of spermatogenesis. Using SDS-PAGE analysis, 13 bands were identified, most of which migrated between 20 to 60 kDa. In the last weeks of treatment significant increases were observed in the percentage of motile spermatozoa, curvilinear velocity and beat cross frequency. This improvement in sperm quality coincided with a higher amount of proteins located at 19 KDa, therefore, this protein could be involved in sperm motility of the European eel.