Ovarian maturation was studied in pond-reared and wild-caught specimens of the shrimp Penaeus kerathurus in order to evaluate the influence of extensive culture conditions on the reproductive capacity of this species. 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 weight were recorded, and the gonadosomatic index (GSI) calculated. Once dissected out and weighed, the ovaries were processed for histological examination. The size reached by the shrimp reared in the pond was comparable to that recorded in the wild. However, significant differences were found in the GSI and the frequency (expressed as percentage) of 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 histological anomaly detected in all pond-reared shrimp examined was the absence of fully mature oocytes, which is due to the inability of late vitellogenic oocytes to synthesize cortical rods. Consequently, stage IV ovaries (characterized by the presence of mature oocytes i.e., those bearing cortical rods) were not found in captive animals. As the cortical rods are believed to play an important role at early development in penaeid eggs, their absence is probably one major constraint resulting in a broodstock population with reduced reproductive potential under culture conditions.

This work has been supported by grant AGF93-0173 of the CICYT (Comisión Interministerial de Ciencia y Tecnología).

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Peer reviewed