Condition factor variations over time and trophic position among four species of Characidae from Amazonian floodplain lakes: effects of an anomalous drought.

I A Tribuzy-Neto,K G Conceição,L E Hurd,C E C Freitas,F K Siqueira-Souza

doi:10.1590/1519-6984.166332

Abstract

The effects of extreme droughts on freshwater fish remain unknown worldwide. In this paper, we estimated the condition factor, a measure of relative fitness based on the relationship of body weight to length, in four fish species representing two trophic levels (omnivores and piscivores) from Amazonian floodplain lakes for three consecutive years: 2004, 2005 (an anomalous drought year), and 2006. The two omnivores, Colossoma macropomum and Mylossoma duriventre, exhibited trends consistent with their life cycles in 2004 and 2006: high values during the hydrologic seasons of high water, receding water, and low water, with a drop following reproduction following the onset of rising water. However during the drought year of 2005 the condition factor was much lower than normal during receding and low water seasons, probably as a result of an abnormal reduction in resource availability in a reduced habitat. The two piscivorous piranhas, Serrasalmus spilopleura and S. elongatus, maintained relatively stable values of condition factor over the hydrologic cycles of all three years, with no apparent effect of the drought, probably because the reduction in habitat is counterbalanced by the resulting increase in relative prey density. We suggest that if predictions of increasing drought in the Amazon are correct, predatory species may benefit, at least in the short run, while omnivores may be negatively affected.

Highlights

The effects of extreme droughts on freshwater fish remain unknown worldwide
The composite data do not show the variations that occurred in the weight-length condition factor index
For C. macropomum, this interaction effect can be identified with the anomalous drought of 2005

Summary

Introduction

The effects of extreme droughts on freshwater fish remain unknown worldwide. In this paper, we estimated the condition factor, a measure of relative fitness based on the relationship of body weight to length, in four fish species representing two trophic levels (omnivores and piscivores) from Amazonian floodplain lakes for three consecutive years: 2004, 2005 (an anomalous drought year), and 2006. The two piscivorous piranhas, Serrasalmus spilopleura and S. elongatus, maintained relatively stable values of condition factor over the hydrologic cycles of all three years, with no apparent effect of the drought, probably because the reduction in habitat is counterbalanced by the resulting increase in relative prey density. As piranhas Serrasalmus spilopleura e S. elongatus, mantiveram relativa estabilidade nas estimativas do fator d condição, ao longo do ciclo hidrológico dos três anos, sem efeito aparente da seca extrema, provavelmente porque a redução do habitat foi contrabalanceada pelo aumento na densidade de presas. The aquatic environment of the Amazonian floodplains in Brazil contains thousands of lakes and associated wetlands that are interconnected to varying degrees, forming a huge and complex drainage network These environments are highly dynamic, with an annual hydrologic cycle known as the flood pulse (Junk et al, 1989). Lakes diminish in depth and area during the low-water season, with a consequent decline in habitat and food availability

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Results

Conclusion