CHANGES IN THE STEROID-HORMONE AND VITELLOGENIN LEVELS DURING THE GAMETOGENIC CYCLE OF THE GIANT TIGER SHRIMP, PENAEUS-MONODON

The levels of estradiol-17 beta, and progesterone in the hemolymph, ovaries and hepatopancreas, in relation to the vitellogenin levels of captive female Penaeus monodon, were determined during the gametogenic cycle. Estradiol in the hemolymph was detected in fully mature shrimps (Stage 5) only. The ovarian estradiol levels were quite variable but showed no significant differences in the mature (Stages 4 and 5) and spent stage (Stage 6). In the hepatopancreas, a peak in estradiol level was noted in mature shrimps (Stage 5). The progesterone levels in the hemolymph were high in shrimps with mature ovaries (Stages 4 and 5) while those with immature ovaries (Stages 2, 3 and spent) were low or undectectable. The progesterone levels in both ovaries and hepatopancreas were significantly high in mature shrimps. The vitellogenin levels increased simultaneously with ovarian development and reached maximum levels during the final stage of vitellogenesis. A decrease in levels was observed after egg release. The correlation between the levels of progesterone and vitellogenin may indicate a positive effect of this steroid on vitellogenin production.