Influence of abiotic factors on ichthyoplankton occurrence in stretches with and without dams in the upper Grande River basin,south‐eastern Brazil

The influence of abiotic factors on ichthyoplankton occurrence was assessed in lotic stretches with and without dams in the Grande River basin from November 2008 to March 2009. Water transparency and temperature were the main abiotic factors that influenced temporal variation of ichthyoplankton occurrence in unregulated stretches. On the other hand, the best predictors of ichthyoplankton occurrence in regulated sites were water transparency and time of day. The catch of ichthyoplankton was significantly greater at low transparency and during night‐time in areas downstream of dams, which may be attributed to either adaptive behaviour of fish species in favouring greater protection of offspring, or the greater predation rate of ichthyoplankton at higher transparencies and during daytime. Results of this study indicate an association between abiotic factors and fish reproduction, but the nature of this relationship in regulated rivers contrasts with that found in stretches without dams.