ABSTRACT:
Vitellogenin (Vg), the yolk precursor protein, which has many other physiological functions than its primary role of providing nutrients to the embryos, was utilized to promote somatic growth and testicular function in juvenile male catfish Clarias gariepimus during preparatory (Feb-Apr) and prespawning-spawning (Nay-Aug) periods in the laboratory under normal conditions. Three semipurified catfish (Clarius batrachus) Vg-pellets (100 pg/pellet) implantations at 30 days interval to juvenile male catfish (Clarias gariepinus) brought about somatic growth without effecting the plasma growth hormone (GH) levels during preparatory period, whereas during prespawning-spawning period there was no such growth promoting effect was noticed. However, a low but significant increase in plasma GH levels was observed in Vg-implanted group. Vg. implantation was ineffective in influencing testicular growth but histological observations revealed the occurrence of active spermatogenesis with large number of spermatozoa in seminiferous tubules during both periods. There was a trend of increase in plasma testosterone (T) levels in Vg-implanted catfish during prespawning-spawning period but no such changes were noticed during preparatory period. The results, thus, indicate that both somatic growth and spermatogenesis induced by Vg-implantation within 90 days in juvenile male catfish may be through the production of T and GH secretion in an unknown manner. Further work is necessary in this fish and also in other fish species to focus on the exact mechanism of Vg-action on somatic growth and development of gonads.