Effect of leucine enkephalin administration on ovarian maturation in the freshwater crab Travancoriana schirnerae
The current study focused on the effect of administration of the neurotransmitter leucine enkephalin on ovarian maturation in the freshwater crab Travancoriana schirnerae .  The crabs were administered with leucine enkephalin in multiple doses (10 µl/injection) and their dissected ovaries were processed for histomorphological analyses. Ovarian maturation was assessed by both macroscopic and microscopic observations such as ovarian index, mean oocyte diameter, oocyte proportion values and histological examinations of the ovaries of control and treated crabs. Our observations revealed significantly higher ovarian index, oocyte diameter and oocyte proportion values in treatments over controls. Leucine enkephalin treatment induced previtellogenic ovary to grow into primary vitellogenic, primary vitellogenic to secondary vitellogenic 1 secondary vitellogenic 1 and 2 to secondary vitellogenic 3 stage as evinced by the presence of a large number of primary previtellogenic ovaries in previtellogenic oocytes, larger proportion of secondary vitellogenic oocytes in primary vitellogenic ovaries and secondary vitellogenic stage 3 oocytes in secondary vitellogenic stage 1 ovaries of treated crabs over the controls. The conversion of previtellogenic ovary to early vitellogenic, early to middle and middle to late vitellogenic ovaries in treated crabs probably indicate the stimulatory effect of leucine enkephalin on ovaries either by triggering the release of the gonad stimulating hormone synthesized and released from the brain or thoracic ganglion or by blocking the release of the gonad inhibiting hormone synthesized and secreted by the X organ-sinus gland complex of the eyestalks or both. The results of the present study clearly indicate that leucine enkephalin has a stimulatory effect on ovarian maturation in T. schirnerae , thus shortening the period of maturation of ovary, which can be utilized in large-scale production of the species concerned. Further studies are needed to check the efficacy of this neurotransmitter as a supplement in diet to induce ovarian maturation of this species.