Seasonal growth and life history of the catfish Calophysus macropterus (Lichtenstein, 1819) (Siluriformes: Pimelodidae) from the Amazon floodplain

The objective was to study seasonal aspects of the piracatinga catfish ( Calophysus macropterus ) growth and its relationship with the flood pulse. Analyzed from June 1997 to May 1998 were 446 specimens from the Amazon River. Using the period regression model with several biometric indexes gave the following results: two periods of low growth were identified in the vertebrae of C. macropterus , the first during falling water (August) and the second during rising water (January), using marginal increment analysis (MIA). This pattern was also observed in the annual variation of the regression coefficient of the length–weight relationship ( b ), and Feeding Index (FI), but an inverse relationship was observed with the Maturity Index (MI). These results suggest that reproduction occurs from January to February in the rising water season, when C . macropterus reaches sexual maturity at 1.4 and 1.5 of age for females and males, respectively. The parameters of Bertalanffy's model were SL = 40.05[1−e^{−0.44(t−0.37)}] for females and SL = 41.9[1−e^{−0.42(t−0.36)}] for males. Natural mortality was high (♀:0.42–♂:0.40) and longevity low (♀:6.8–♂:7.1 years). The present study demonstrates that seasonal growth in C. macropterus is correlated with the flood pulse, especially in periods of rising and falling waters. These results, analyzed by the periodic regression model, showed that reproduction, migration or changes in feeding behavior have relationships with annulus formation in hard structures in this species. All quantitative indexes show clear seasonal variation to be correlated with river water level fluctuations.