Vila, Y., A. Medina
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 5 female shrimps were taken from the wild and 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) was calculated. Afterwards, the ovaries were processed for histological examination. The diameter and percentage of three distinct oocyte categories were measured.
The size reached by individuals reared in the pond was comparable to that recorded in the wild. However, significant differences were found in the GSI and the frequency of postvitellogenic (i.e., vitellogenic plus mature) oocytes, which may be considered as good indicators of the sexual maturation rate. Five distinct stages (I-V) have been distinguished throughout the process of ovarian maturation. A major histological anomaly detected in all pond-reared shrimps sampled is the absence of fully mature oocytes, which is due to the inability of late vitellogenic oocytes to synthesize cortical rods. Consequently, stage IV ovaries were not found in captive animals. As cortical rods are believed to play an important role at early penaeid egg development, their lack probably results in reduced reproductive potential under culture conditions.
(Depto. de Biologia Animal, Vegetal y Ecologia, Facultad de Ciencias del Mar, Universidad de Cadiz, Poligono del Rio San Pedro, s/n, Apartado 40, E-11510, Puerto Real, Cadiz, Spain)
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