Fish Eggs and Larvae Occurrence and Abundance in a Southeastern Brazilian River System

We associated the density of ichthyoplankton with abiotic environmental variables using predictive models in the Paraíba do Sul River (RPS) and its tributaries, a river system that runs through one of the most industrialized regions of Brazil. About 80 fish species occur in the system, of which migratory species are main fishery targets. Samples were collected (surface/bottom, day/night) in 2011 and 2012 in the Fluvial Islands Domain (FID), lower-middle portion of the RPS, near the confluences of the Pomba (RP) and Negro (RN) rivers. Dissolved oxygen, temperature, conductivity, pH, transparency, depth and flow were measured. We captured 2.458 eggs and 1.059 larvae. The highest abundance was in RP (74.41% of eggs and 69.69 % of larvae), followed by RPS (20.22%, 16.05%) and last in RN (5.37 %, 14.26 %), with higher abundance at night. Generalized linear models for egg and larvae density (abundance/volume filtered) explained around 50% of variation, with positive coefficients for flow, pH and conductivity, and negative for DO, temperature, depth and transparency. Density peaks were correlated with the start of the rainy season, but the model coefficients also show partial effects of the variables. The predominance of eggs indicates the importance of the FID as spawning grounds.