This study concerns the reproductive strategy of the freshwater fish, Leporinus piau, native to the Brazilian semi-arid region. The hypothesis of this work predicts that the species would spawn during the rainy season, presenting a seasonal reproductive strategy. The study investigated the structure of total body length and body mass, sex ratio, body size at first sexual maturity, developmental stages of gonads, fecundity, gonadosomatic index (GSI), condition factor (K) and the spawning season of L. piau. Twelve monthly samplings (mean n = 18) were carried out in 2009 and environmental parameters such as rainfall, temperature, pH, electrical conductivity and concentration of dissolved oxygen of water were registered. The sampled population of L. piau (n = 211) showed a slight predominance of males (55%), but with larger and heavier females. First sexual maturation in males occurred earlier (16.5 cm total length) than in females (20.5 cm total length). The species is a total spawner with an average fecundity of 55 000 mature oocytes. Rainfall (225 ± 7.2 mm) and concentration of dissolved oxygen (8.5 ± 0.2 mg L−1) acted as influential factors during the spawning season. The monthly GSI shows that spawning starts when the rainy season is at its maximum and ends synchronously (females r = 0.91; males r = 0.89) with the end of the rainy season. L. piau presents a seasonal reproductive strategy with high reproductive output, providing a population increase and exploitation of the environmental resources.