Some aspects of the ecology of fish larvae in the floodplain of the high Paraná river, Brazil

Abstract

ABSTRACT. The spatial and temporal distribution and nychthemeral variation oftish larvae in six stations (Ivinhema, Patos, Parana, Cortado, Baia and Guarana) in the floodplain of the high Parana river arc provided. The paper a lso provides the relationship of this distribution to some environmental factors. From March 1992 to February 1993 ichthyop lanktonie samples were collected by conic cylind ri cal nets, with 0.5mm of mesh size and tluxometer attac hed, in I O-minute hau ls at the surface and bottom during nychthemeral cycles. At th e same time water samp les were taken to determine environmental factors. During the above period 5,672 larvae were collected: 57,6% fi·Ofll Cortado station and 13 ,2% fromlvinhema and Parana stati ons. The greatest densities were recorded between October and February, chi efly at night at the surface and by day at the bottom. KEY WORDS. Fish larvae, ecology, distribution, floodplain, Parana river Floodp lains are areas seasonal ly submitted to severe modifications in their physical, chemical and hydrological charactcristics and in their animal and vegetal communities. These changes are incorporated to the life cycle of various species . In the flood periods when the water volume transported by the river is very great, the decomposition of vegetation, animal excrements, autochthonous and allochthonous organic material cause a considerable enrichment of the water due to the great quantity of organic and inorganic nutrients produced in the process. This factor greatly favours the proliferation of bacteria, phytoplankton and zooplankton, organisms that uphold a rich fauna of invertebrates and vertebrates in all the environments of the floodplain. The biomass is heavily exploited by fish in their initi al phases of development causing their rapid growth, bypassing the stages most vulnerable to predation.For a better understanding of the environmen tal mechanisms that influence the behaviour of fishes it is necessary to know the relationship between the occurrence and the distribution of eggs and larvae and the environmental conditions of spawning and growth areas. It is also necessary to register an nual oscillations and to detect tendencies ofa community, populat ion or stock throughout a certain period of time. This will result in a bettering of knowledge on reproduction, ontogeny and taxonomy of these groups

Spatial and temporal distribution patterns of ichthyoplankton in a region affected by water regulation by dams

“…Baumgartner et al (1997), Bialetzki et al (2004) and Baumgartner et al (2008) found similar results to that obtained in this study. Baumgartner et al (2008) showed in their conceptual model that the larvae of different species have different relationships with abiotic variables.…”

Spawning areas, dispersion and microhabitats of fish larvae in the Anavilhanas Ecological Station, rio Negro, Amazonas State, Brazil

“…These results are similar to many others of diurnal distribution and abundance of ichthyoplankton in tropical rivers (Baumgartner et al, 1997;Araújo-Lima et al, 2001;Bialetzki et al, 2004) and in temperate regions (Gale & Mohr, 1978;Hergenrader et al, 1982;Gallagher & Conner, 1983;Corbet & Powles, 1986;Gadomski & Barfoot, 1998). Baumgartner et al (2004) studying larvae of Hypophthalmus edentatus, Plagioscion squamosissimus and species of Characiformes in the upper Paraná River mentioned the interaction of several factors that act in the highest capture at the surface at night, but they affirm that the feeding activity would trigger the whole process of vertical distribution.…”

“…A decrease followed by an increase in the values of the temperature and electrical conductivity of the water are pointed out as "triggers" for spawning in tropical rivers (Nakatani et al, 1993;Vazzoler, 1996;Baumgartner et al, 1997;Bialetzki et al, 2004). Nevertheless, another factor that could influence the decrease in the capture of eggs is the short time between incubation and eclosion.…”

Spatial and temporal distribution of ichthyoplankton in the upper Uruguay river, Brazil

“…Pearson's correlation showed a negative influence of hardness on the distribution of eggs, and a positive influence of water temperature and transparency on the distribution of larvae (Table 5). As observed by other authors (Nakatani et al, 1993;Baumgartner et al, 1997;Bialetzki et al, 1999), abiotic factors significantly influence the early life stage of fish. In the Paraná river basin, an increased abundance of some larval species was observed when the water temperature was higher, pH was increased, dissolved oxygen concentration was reduced drastically (Nakatani et al, 1993), and the electric conductivity was at its highest values .…”