Population structure and reproduction of Steindachneridion melanodermatum (Siluriformes: Pimelodidae), a large catfish endemic to Neotropical ecoregion

The population structure and reproductive biology of the surubim of Iguacu, Steindachneridion melanodermatum, a large endemic and endangered catfish from Iguacu River basin, were evaluated. In total, 182 specimens of this species were sampled from September 2010 to December 2016 in the Lower Iguacu River, including some tributaries. The determination of the cycle and reproductive period was undertaken by assessing the mean variation in the values of the gonadosomatic index (GSI) of females and males, as well as by the frequency distribution of the stages of gonadal development on the basis of macroscopic and microscopic analyses. The total length and bodyweight ranged from 21 to 102cm and from 82.8 to 15670g respectively. The reproductive period of this species was from June to September (winter and early spring), and may extend until November, with GSI peaking in August for males and September for females. The size at first maturation (L50) corresponded to 39.5cm for females and 43.9cm for males. Spawning in this species was associated with lower water temperatures, and high discharge and dissolved oxygen concentration. Our findings are crucial in assisting the development of effective measures and specific criteria for the conservation of this endangered species.