Information regarding the reproductive cycle of commercially exploited fish species is extremely important for their appropriate management. The reproductive size of Pinirampus pirinampu (Spix, 1829) was determined for a population studied in the Pantanal wetlands of western Brazil. Samples were taken in September, October, and December 1997, and in February and March 1998. Gonadal stages were macroscopically determined and a monthly gonadossomatic index (GSI) was used to determine the breeding period. The length of the first gonadal maturation was determined by classifying male and female adults and immature fish into length classes. The data on the adult individuals were plotted on graphs and the median values estimated to find the length at which 50% of the individuals reached maturity (L50). L100 was also determined. Males and females in the gonadal maturation process were recorded from October on, and the highest frequency was found to occur in February. Individuals with empty gonads occurred from February onwards. The GSI showed that gonadal development began in September and reached its peak in February. The L50 was 574 mm for females and 536 mm for males, while the L100 was 590 mm for females and 580 mm for males.
reproduction; Pinirampus pirinampu; Pantanal
