A COMPARATIVE-STUDY OF THE OVARIAN DEVELOPMENT IN WILD AND POND-REARED SHRIMP, PENAEUS-KERATHURUS (FORSKAL, 1775)

Ovarian maturation was studied in pond-reared and wild-caught specimen s of the shrimp Penaeus kerathurus in order to evaluate the influence of extensive culture conditions on the reproductive capacity of this s pecies. Monthly samples of five female shrimp were taken from the wild and the pond from late winter (February-March) to mid-summer (July). For each specimen sampled, the body length, body weight and ovarian we ight were recorded, and the gonadosomatic index (GSI) calculated. Once dissected out and weighed, the ovaries were processed for histologica l examination. The size reached by the shrimp reared in the pond was c omparable to that recorded in the wild. However, significant differenc es were found in the GSI and the frequency (expressed as percentage) o f postvitellogenic (i.e. vitellogenic plus mature) oocytes, which may be considered as good indicators of the sexual maturation rate. On the basis of the overall gonad histology, five distinct stages have been identified throughout the process of ovarian maturation. A major histo logical anomaly detected in all pond-reared shrimp examined was the ab sence of fully mature oocytes, which is due to the inability of late v itellogenic oocytes to synthesize cortical rods. Consequently, stage I V ovaries (characterized by the presence of mature oocytes, i.e., thos e bearing cortical rods) were not found in captive animals. As the cor tical rods are believed to play an important role at early development in penaeid eggs, their absence is probably one major constraint resul ting in a broodstock population with reduced reproductive potential un der culture conditions.