The chemical nature of sex attracting pheromones from the seminal vesicle of the African catfish, Clarias gariepinus

In attraction tests, ovulated female African catfish, Clarias gariepinus, were attracted by the administration of 2.0 ml/l seminal vesicle fluid to the aquarium water. Lower doses (0.1 and 0.5 ml/l) were ineffective, and a high concentration (8.0 ml/l) seemed to have a repulsive effect. After fractionation of the fluid, an isolated steroid conjugate fraction appeared to contain the attractant. No other stimuli beyond this fraction were required to attract groups of female catfish after ovulation. Other constituents of the fluid such as polysaccharides, proteins, phospholipids and steroids failed to attract the females. GCMS analysis of the steroid conjugate fraction revealed the presence of eight different steroid glucuronides. After removal of these steroid glucuronides, the steroid conjugate fraction lost its attractive effect. A mixture of seven available synthetic steroid glucuronides was composed according to the quantitative results of the GCMS analysis. This mixture appeared to have a powerful dose-dependent attractive effect on ovulated females. It is concluded that a combination of various steroid glucuronides, present in seminal vesicle fluid, functions as a sex attractant, bringing male and female African catfish together shortly before spawning.