Reproductive status in females of the Brazilian catfish, Pseudoplatystoma fasciatum reared in cages

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Summary The distinctive morphological features of the ovaries the ‘cachara’, Pseudoplatystoma fasciatum were characterized macroscopically, and by histology, when reared in cages, from March 2005 to February 2006. Forty eight females (mean total weight = 2.7 kg, mean standard length = 65.1 cm) were allocated to four cages of 2.7 m3 (20 fish/cage) which were installed in four 600 m2 ponds, located at the IP, Pariquera-Acu, Sao Paulo, Brazil. The monthly, samples were fixed in 4%-buffered formalin before preparation for histological examination, ovaries were removed and weighted. The gonadosomatic index (GSI) was calculated as = 100 × weight ovaries/total fish weight. The ovaries are the cystovarian type and macroscopically, were established three stages of ovarian maturation: Resting, developing Maturation (initial, intermediate, final) and Regression (initial, intermediate, final). Based on morphological criteria of those ovaries, the oocyte development has been divided into distinct stages: (i) oocyte growth (vitellogenesis); (ii) oocyte maturation, along which it goes through different phases of development, before (iii) ovulation and, (iv) spawning. When the P. fasciatum were kept in confinement and not induced to breed occurs fail to attain final oocyte maturation, start the process of degeneration. Consequently, the weight started to decline and 45% of the ovaries showed atresia of vitellogenic follicles. This was considered indicative of a recent cessation of the reproductive activity. Such failure could have been caused by stress of the monthly sampling involving a certain degree of disturbance, and perhaps also by the existence of stressors while in captivity. The synchronous ovary contained oocytes in an unique stage of development and had potential to perform total spawning up to one time a year, with the period reproductive beginning in the end of November to the beginning of February, coinciding with the highest water temperatures in the experimental cages (29.0–31.5°C) and the increase of mean values of GSI. During the regression phase, residual oocytes could be observed together with decrease of the mean values of GSI and, the temperatures.