Serine proteinase inhibitors in the seminal plasma of percid fish

In this study trypsin-inhibitory activity of the seminal plasma of percid fish: perch (Perca fluviatilis, n = 22), pikeperch (Sander lucioperca, n = 5), Volga pikeperch (Sander volgensis, n = 7) and hybrid between S. lucioperca ([female symbol]) and S. volgensis ([male symbol]) (n = 11) was identified and measured. Comparison of profiles of anti-trypsin activity (APA) in blood and seminal plasma of perch and hybrid was also performed. Profiles of serine proteinase inhibitors were quite unique in the seminal plasma of percid fish. Instead of 1-3 inhibitors (typical pattern of APA in teleost fish), at least five bands of serine proteinase inhibitors with different migration rates were detected. Proteinase inhibitors profiles and other parameters of the hybrid semen were close to values of the pikeperch (maternal species). Perch and hybrid seminal plasma proteinase inhibitors migrated during electrophoresis similarly to blood plasma proteinase inhibitors. A significant correlation between seminal protein concentration and APA was confirmed for percid fish (r² = 0.78, P < 0.001 and r² = 0.93, P < 0.01, for perch and Volga pikeperch, respectively). Further studies are necessary to elucidate molecular basis of APA heterogeneity in percid fish in order to identify families of these inhibitors and to understand their possible physiological roles.