Assessment of an ichthyoplankton net operated at different velocities and durations in the Paraná River

Abstract

The aim of this work was to evaluate the performance of a conical ichthyoplankton net under the most common range of sampling conditions found in the Paraná River. Three sampling velocities in the range of 0.3-1.4mseg-1 and four sample durations (2, 4, 8 and 16min) were simulated from two different experiments carried out in surface and bottom waters of the main channel during daylight hours. Neither significant differences nor trends were found in larval fish densities in various stages of development under the conditions studied. Results are discussed in the context of the natural ichthyoplankton abundance variability. The results support the hypothesis that in turbid waters larvae are not visually able to detect the net and that in the size range sampled, they either cannot mechanically detect the gear or have not developed enough swimming ability to efficiently evade it. The results of this work may contribute to the interpretation of the abundance data in ichthyoplankton studies in South American rivers with similar ranges of transparency, flow and larvae development.