Abstract
This study aimed to know the daily variation of Astyanax lacustris (Lütken 1875) feeding in a lotic environment. Fish were caught with a net for three days every three hours in the summer to capture ten individuals per hour in a stretch of the Ijuí River, Middle Uruguay River, Brazil. The captured specimens had their stomachs removed and the content analyzed and separated into seven food categories with the aid of stereomicroscope. For the analysis of food items were used the frequency of occurrence methods, volumetric method and applied the Alimentary Index (IAi). Two hundred stomachs were analyzed, of which 95% had food content. The most abundant items were algae and autochthonous insects. Astyanax lacustris feeds throughout the day especially early in the morning (9 hours) and reduces its feeding at night (24 hours and 3 hours). It was also verified variation of AI of different food items throughout the day. It is concluded that A. lacustris feeds throughout the day, especially in the daytime and that throughout the 24 hours it varies its diet due to photoperiod and food availability.
Highlights
Neotropical ichthyofauna is characterized by high feeding flexibility, using a wide variety of alimentary resources present in the aquatic environment and even terrestrial environment (Petry, Thomaz, & Esteves, 2011; Meurer & Zaniboni-Filho, 2012)
The present study aimed to evaluate the A. lacustris diet at different times of the day, supposing that A. lacustris in Middle Uruguay presents a daily variation in the quantity and quality of its feeding, based on studies with other species (Hahn, Loureiro, & Delariva, 1999; Figueiredo & Vieira, 2005)
The category others was composed of the digested material that composed most of the rare items of small value, such as feathers, insect eggs, free-living nematodes, annelids, arachnids, and microplastic (< 2.0 mm)
Summary
Neotropical ichthyofauna is characterized by high feeding flexibility, using a wide variety of alimentary resources present in the aquatic environment (microorganisms, primary producers, invertebrates, vertebrates) and even terrestrial environment (primary producers and insects) (Petry, Thomaz, & Esteves, 2011; Meurer & Zaniboni-Filho, 2012). The fish of the genus Astyanax forage all trophic levels, presenting abilities to adapt rapidly to a new feeding and to continue feeding even in unfavorable environmental conditions (Gomiero & Braga, 2003; Corrêa & Silva, 2010). These individuals inhabit the middle and surface strata, either in lentic or lotic waters, to collect items dragged by the water, characterized by frequent omnivorous feeding (Gomiero & Braga, 2003; Falcón et al, 2010)
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