Seminal vesicle secretion of African catfish, its composition, its behaviour in water and saline solutions and its influence on gamete fertilizability.

The seminal vesicle secretion (SVS) of the African catfish, Clarias gariepinus, was investigated by analytical and experimental methods. SVS consists mainly of proteins and glycoproteins which are responsible for its viscous and sticky nature. The secretion contains also high activities of acid phosphatase, alkaline phosphatase, and proteases. These catabolic enzymes do not have functions in autolysis or liquefaction of SVS but are considered to eliminate aging spermatozoa from the proximal portions of seminal vesicle and from the spermatic duct. SVS of the African catfish is unstable in the environment relevant for natural spawning. When SVS was mixed with water, seminal plasma or different types of saline solutions its protein coagulated forming fibrous or granular particles of variable size within a few seconds. Pure SVS completely inhibited the motility as the sticky secretion hindered spermatozoa in free swimming. SVS had also a negative effect on sperm fertility, egg fertility, and sperm egg contact, as the fertilization was drastically suppressed in the presence of SVS. Basing on our analytical and experimental results we exclude that SVS has functions in stabilizing the viability of spermatozoa stored in the spermatic ducts or is an energy resource of spermatozoa. It also does not improve or stabilize the fertilization process and has no functions in adhering the eggs to substrates or in covering the eggs for mechanical protection or antibacterial defense. A function of SVS in the male and female communication during the prenuptial spawning behaviour is discussed.