Abstract
Understanding of aspects of the structure of ichthyological communities and how these relate to the environment and its natural variation has been one of the principal objectives of ecological studies conducted in freshwater environments. The objective of this study was to evaluate the relationship between fish species composition in the Una River and environmental variables during dry and rainy seasons. Data collection was done along three stretches of the main channel of the Una River between April 2016 and March 2017. In general, the riverbed presented a high degree of silting in all study sites. A total of 1,534 fish specimens from thirty species were collected. There was greater richness and abundance of species during the rainy season in all sampled areas. A Partial Redundancy Analysis (pRDA) showed a significant correlation between the fish community, substrate composition, and concentrations of dissolved oxygen in the water. The qualitative structure of the ichthyofauna indicated a greater association with environmental structure than with seasonality, since there was a clear tendency for the three stretches of river to group together independent of the sampling period. There were no significant differences between the indices of diversity registered for the dry and rainy seasons. This is due to the dominance of the species Astyanax aff. bimaculatus (two spot Astyanax | lambari-do-rabo-amarelo) and Hypostomus cf. luetkeni (armoured catfish | cascudo), which represented more than half of the collected specimens during the rainy season.
Highlights
Understanding of structural factors of ichthyological communities and how these relate to the environment and its natural variation has been one of the principal objectives of ecological studies conducted in freshwater environments (Giller and Malmqvist, 1998)
Habitat structure and temporal changes in environmental conditions are recognized as being able to influence patterns of fish species composition and distribution, especially in small rivers and streams where species are highly dependent on structural components of the aquatic environment for survival (Poff, 1997; Allan, 2004; Kovalenko et al, 2012)
Environmental parameters With respect to the environmental parameters evaluated in this study, each sampled stretch of the river demonstrated its own unique characteristics in terms of substrate composition, depth, and current velocity
Summary
Understanding of structural factors of ichthyological communities and how these relate to the environment and its natural variation has been one of the principal objectives of ecological studies conducted in freshwater environments (Giller and Malmqvist, 1998). Branches, and leaves increase structural complexity of bodies of water as these serve as refuge from predators, shelter from strong currents, places for egg deposition and development of juvenile fish, besides providing a variety of food sources (Angermeier and Karr, 1984; Crook and Robertson, 1999; Casatti et al, 2012; 2015) Limnological characteristics, such as water temperature, pH, and levels of dissolved oxygen exert great influence on distribution of fish species due to their particular physiological characteristics (Angermeier and Karr, 1984; Pulsey and Arthington, 2003; Allan and Castillo, 2007; Ferreira et al, 2014). Such changes tend to influence the structure and composition of local assemblages through habitat availability and ecosystem productivity, establishing connections between bodies of water in adjacent areas during the period of greater rainfall, or isolating these habitats during dry periods (Power et al, 2008; Jardine et al, 2015; Fitzgerald et al, 2017; Sabo et al, 2017)
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