Variação diária da alimentação do Lambari Astyanax lacustris no Rio Ijuí, RS, Brasil

Abstract

The rate of food intake and fish utilization are directly related to feeding time. Studies on daily variation in diet allow observing patterns in their behavior at different times of the day. In this sense, the objective of this work was to know the daily variation of the feeding of the species Astyanax lacustris in a lotic environment. The collections were carried out on a stretch of the Ijuí River known as the Pirapó Jump (Middle Uruguay River Basin, Brazil), during three days in the summer season of 2017 at different times: 06h, 09h, 12h, 15h, 18h, 21h, 24h and 03h. The fish collection was carried out with a casting net, in order to capture ten individuals per hour. The captured individuals had their stomachs removed and fixed in 4% formaldehyde to later proceed with the analysis of the stomach contents in the laboratory. The identification of the organisms consumed by the fish was carried out using a stereomicroscope microscope and specialized bibliography for the analysis in the following groups: Fish, allochthonous insects, autochthonous insects, algae, plant material, sediment and others. After identification of the stomach contents, the items were stored in 70% alcohol. For the analysis of food items, the frequency of occurrence, volumetric and food index methods were used. The analysis of variance (ANOVA unifatorial) and a posteriori test of Tukey were used to verify differences in feeding at different times. A total of 200 stomachs were analyzed, of which 86.5% were full and 5% partially full, 3% partially empty, 5% empty and 0.5% distended. Different food items were found including microplastic, the most present items were algae and autochthonous insects. A. lacustris feeds all day long mainly at the beginning of the morning (9h) (V = 3,280mm, P <0,05) and reduces its feeding during the night 24h (V = 478mm) and 3h (V = 361mm). It was verified a variation of IA of the different food items throughout the day, being verified a greater consumption of autochthonous insects at 9h and 21h (P <0.05), algae between 6h and 18h (P <0.05), material (P <0.05), allochthonous insects between 21h and 24h (P <0.05) and fish between 9h and 3h (P <0.05). It is concluded that A. lacustris is fed throughout the day, mainly during the daytime period and that during the 24 hours it changes its diet according to the photoperiod and the greater availability of the organisms in the environment.