Annual cyclic, and castration and cyproterone acetate-induced, changes in sialic acid content of the seminal vesicle of the catfish, Heteropneustes fossilis (Bloch).

In this study, the presence of sialic acid is demonstrated in the seminal vesicle (SV) of Heteropneustes fossilis. Sialic acid levels show an annual variation that was correlated with the secretory activity of the SV (expressed as the SV somatic index (SV-SI)) with the index being lowest in resting phase (January) and highest in spawning phase (July). Sialic acid was not detectable from November to March (resting to mid-preparatory phases). Castration (3 weeks) induced a significant rise in both SV-SI and SV sialic acid content possibly due to an elevated local production of androgens under the influence of increased gonadotropin secretion. Cyproterone acetate treatment caused a significant decrease in both SV-SI and SV sialic acid content. The results suggest that secretion of sialic acid in the SV is influenced by androgens and its measurement can be used as a simple and reliable index for quantitative assessment of the functional testicular state.