Reproductive strategy of Leporinus piau (Fowler, 1941), a neotropical freshwater fish from the semi-arid region of Brazil By W. Silva do Nascimento, A. Soares de Arau´jo, N. T. Chellappa and S. Chellappa Postgraduate Program in Psychobiology, Departamento de Oceanografia e Limnologia, Centro de Biocieˆncias, Universidade Federal do Rio Grande do Norte, Lagoa Nova, Natal, Rio Grande do Norte, Brazil Summary This study concerns the reproductive strategy of the freshwa- ter 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 con- ductivity 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 lar- ger 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 À1 ) 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 syn- chronously (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 popula- tion increase and exploitation of the environmental resources. Introduction The seasonality of the freshwater ecosystems in Northeastern Brazil is due to recurrence of extended drought, irregular rainfall, high temperatures and an elevated rate of water evaporation. This region receives almost 750 mm of annual rainfall and has an average annual temperature of 26°C throughout most of the region (Silva, 2004). The native freshwater fish Leporinus piau (Fowler, 1941) of the semi-arid region is widely distributed in the hydrographic basins of northeastern Brazil (Garavello and Britski, 2003; Chellappa et al., 2009, 2011; Nascimento et al., 2011) and is important for commercial and sport fishing as well as being a great potential for aquaculture, besides being ecologically important as a foraging fish (Alvim and Peret, 2004). Two reproductive strategies based on the various environ- mental resources available are the ‘r’ and ‘K’ strategies, whereby r refers to the strategy involving many small and fecund organisms, and K to the opposite condition (MacArthur and Wilson, 2001). In reality, most habitats offer intermedi- ate conditions so that animals tend toward either the r end of the spectrum or the K end. When resources start to deplete, the capacity of the population to increase becomes impaired. Thus under these conditions fitness is the success with which the population procures sufficient limited resources to enable survival. Tropical fishes under the influ- ence of seasonal rainfall show a pattern as regards their allo- cation of time and resources to reproduction (Chellappa et al., 2009). The present study investigated the structure of total length and body mass of both sexes, the 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. Studies on reproductive biology of fish species are important to provide the necessary infor- mation for fisheries and aquaculture development programs in natural and artificial environments. This study was based on the hypothesis that L. piau, a fish species from the semi-arid region, spawns during the rainy season, which would represent a seasonal reproductive strat- egy. Addressing this hypothesis were: Does the spawning of this species actually coincide with the rainfall in the region? Which reproductive strategy is adopted by this species? Materials and methods Sampling was carried out on a monthly basis from January to December 2009, in the Marechal Dutra Reservoir, RN, Northeastern Brazil (6°26′11″S; 36°36′17″W). The reservoir has an accumulation capacity of 40 9 10 6 m 3 with maximum depth of 25 m and mean of 8.5 m. Fish were captured using 50 m long and 2 m high gill nets with different mesh sizes (varying from 6 to 12 cm) and a 12-h fishing effort. Captured fish were numbered, measured, weighed and samples were used for morphometric measure- ments and meristic counts to confirm the taxonomical identi- fication of the species (Britski et al., 1984). Total length (L t ± 1 cm), total body mass (W t ± 1 g) and gonad weight (W g ± 0.1 mg) were recorded and the sex ratio determined. Young individuals were not included as it was not possible to determine their sex by macroscopic observation. The chi- square test (v 2 ) was applied at a significance level of 5%. Size frequencies were grouped into five classes for total length (L t ), and six classes for body mass (W t ). Body size at first gonadal maturity (L 50 ) where 50% of the individuals exhibited maturing gonads was estimated from the relative frequency distribution of adult males and J. Appl. Ichthyol. (2012), 1–4 © 2012 Blackwell Verlag, Berlin ISSN 0175–8659 Received: November 18, 2011 Accepted: May 20, 2012 doi: 10.1111/jai.12020 Applied Ichthyology Journal of