Identification of fish nursery areas in a free tributary of an impoundment region, upper Uruguay River, Brazil

Abstract

This study aims to determine the importance of different environments of the Ligeiro River (upper Uruguay River, Brazil) in fish reproduction. For this purpose, three environments (sampling sites) were selected: rapids, a pool, and the mouth of the Ligeiro River. Ichthyoplankton, zooplankton, and benthos were sampled six times per month from September, 2006 to March, 2007. Zooplankton and ichthyoplankton samples were collected early in the evening with plankton nets (64 µm and 500 µm, respectively). Benthos samples were also collected early in the evening with a Van Veen dredge. Local abiotic variables (temperature, dissolved oxygen, pH, electrical conductivity, water speed, alkalinity, water hardness, and water transparency) were measured simultaneously with the biotic data sampling and were complemented by regional variables (water flow and precipitation). A total of 43,475 eggs and 2,269 larvae were captured. Of these larvae, 80.1% were in the preflexion and larval yolk stages. Digestive tract content showed that the greatest degree of repletion among the larvae in more advanced phases occurred in the pool environment. Water speed was the main characteristic used to differentiate the river's rapids and mouth from the pool. The abundance of zooplankton and benthos was not related to the distribution of densities among the different components of the ichthyoplankton. A greater abundance of eggs and larvae with yolk was found in the rapids and river mouth. Ordination analyses showed a connection between the advanced stage larvae and the pool environment. In conclusion, the rapids and river mouth of the Ligeiro River's are important locations for fish reproduction, particularly in regard to spawning and drifting of the ichthyoplankton's initial stages, whereas the pool represents a nursery place for larval growth.O presente estudo visa determinar a importância de diferentes ambientes do rio Ligeiro (alto rio Uruguai/Brasil) na reprodução dos peixes. Para isto foram selecionados três ambientes (locais): uma corredeira, um poço e a foz do rio Ligeiro. As coletas de ictioplâncton, zooplâncton e bentos foram realizadas seis vezes por mês, entre os meses de setembro de 2006 a março de 2007. As amostras de zooplâncton e ictioplâncton foram coletadas no início da noite com redes de plâncton com malha 64 µm e 500 µm, respectivamente. A coleta de bentos também aconteceu no início da noite e foi realizada com uma draga de Van Veen. Variáveis abióticas locais (temperatura, oxigênio dissolvido, pH, condutividade elétrica, velocidade da água, alcalinidade, dureza e transparência da água) foram mensuradas simultaneamente as coletas dos dados bióticos e complementadas por variáveis regionais (vazão da água e precipitação). Foi capturado um total de 43.475 ovos e 2.269 larvas; destas, 80,1% se encontravam nos estágios larval vitelino e pré-flexão. O conteúdo do trato digestório das larvas mostrou que o maior grau de repleção das larvas em estágios mais avançados foi encontrado no poço. A velocidade da água foi o principal fator...

Pools and rapids as spawning and nursery areas for fish in a river stretch without floodplains

“…Studies have confirmed the existence of spawning in the region (Reynalte-Tataje et al, 2008a;Hermes-Silva et al, 2009), and more recently, Silva et al (2012) observed local growth and spawning of fish in a tributary located in this region.…”

“…In developing fish stock management and conservation activities, studies involving the first stages of the life cycle of fish are of great importance because the detection of certain stages of their life cycle serves as an indicator of environmental conditions (Copp et al, 1991;Penczak, 1994), as well as helps locating the habitats used by different species in the environment (Silva et al, 2012).…”

“…In this sense, several authors have recognized that knowledge regarding spawning sites and natural nurseries is valuable because it serves as a tool for the protection of fish populations and the management of fishery resources (Nakatani et al, 2001;Silva et al, 2012). Baumgartner et al 612 (2004) also emphasize that the preservation of these sites is of great importance to ensure good recruitment of any species.…”

“…Several models claim that pool environments located in the upper Uruguay River provide favorable conditions for the development of planktonic and benthic organisms, allowing for the growth of fish larvae, while rapids environments may be used as spawning sites and for larval drift (Reynalte-Tataje et al, 2008b;Silva et al, 2012). This study aimed to test this hypothesis and to investigate if the spawning and nursery areas found by Silva et al (2012) in one tributary are also found in other tributaries of the upper Uruguay River.…”

“…This study aimed to test this hypothesis and to investigate if the spawning and nursery areas found by Silva et al (2012) in one tributary are also found in other tributaries of the upper Uruguay River. Accordingly, we have compared the distribution and abundance of fish eggs and larvae in initial stages in two different environments of the Peixe River (upper Uruguay River).…”