The seminal vesicle (SV) and testis of Clarias batrachus (L) exhibit significant annual variations in SVSI and GSI, and in the levels of total proteins, fructose, hexosamines and sialic acid with low values in resting phase and high levels in spawning phase. Histologically, the SV is composed of numerous lobules lined by epithelial cells enclosing a lumen and an interstitial matrix containing interstitial cells (homologous to Leydig cells) and fibroblasts. In the preparatory phase, the SV undergoes extensive growth and proliferation of the lobules (April) with numerous buds of differentiating lobules. With the progress of secretory activity, the epithelial cells which were tall and columnar initially become cubical and squamous. The secretions filled the lumen resulting in distension and enlargement of the follicles and spermatozoa appear in the lumina. After voiding the contents, the SV lobules collapse and degenerate. New lobules are formed from the interstitium by proliferation. They showed transient secretory activity and remained inactive during the resting phase. The increases in total proteins, fructose, hexosamines and sialic acid levels in the SV are directly correlated with the histological changes and secretory activity. The levels of phospholipids and free fatty acids which showed significant variations are low during the spawning phase. The decline in the concentrations of esterified and free cholesterol (EC and FC) in both the testis and SV during the breeding season suggests their utilization as precursors in the synthesis of steroid hormones. The two, however, maintained an inverse relation during the non-breeding season with EC levels high and FC levels low. Scattered spermatogenic cysts in different stages of development are present in the SV epithelium. The similarities in the annual distribution of various biochemical correlates, and the presence of interstitial (Leydig) cells and scattered spermatogenic cysts suggest that the SV has a common origin with the testis and is specialized for secreting a glyco-lipoprotein-rich substance for temporary storage of the sperm.