Ecologia de Astyanax taeniatus na Bacia do Rio Mato Grosso, Saquarema - RJ: Dieta, uso do micro-hábitat e uma breve análise comportamental

Abstract

In this work we aimed to characterize the diet, habitat use and behavior patterns of Astyanax taeniatus at Mato Grosso River Basin. This basin is located in the eastern portion of the State of Rio de Janeiro (22 º 52 'S; 42 ° 40' W and 22 53 'S; 42 ° 34' W). For the diet analysis, the specimens were collected bimonthly between March 2006 and January 2007 in three locations that differed by physical variables. Observations of resource "use" on the habitat were made by underwater observations, on the focal position of the specimens, while the quantification of resource "availability" was performed in 50 quadrats 20x20cm (400cm2) over the same 50m where the underwater observation was made. The analysis of stomach contents of 651 specimens was performed under a stereomicroscope according to qualitative and quantitative methods (Frequency of Occurrence and Volumetric). The proportional contribution of each item recorded in the stomachs for the whole diet was assessed through the Alimentary Index (IAi). To verify possible differences between the proportions of items of animal and vegetable, autochthonous and allochthonous, we used 2 contingency test. From the data of standard length and length of the intestine, we calculated the value of intestinal quotient. Items of plant origin were the major contributors in the diet of the species for locations with higher altitude, while the animal items were the major contributors in the low altitude locality. The difference in the contribution of autochthonous items and allochthonous was also significant. In the diet of youngers and adults, there was a difference in the contribution of items of plant and animal origin only in the highest location, where adults consumed greater amount of vegetable detritus. Mean values of intestinal quotient in youngers and adults were significantly different in places of higher altitude, with higher values for adults. We observed 52% of the individuals at depths between 30 and 45 cm, 72% in areas of rapid, 72% at water velocities between 0 and 0.5 km / h, 66% were distant from the margin between 40 and 120 cm, 37.6 % in the sand substrate and 34.4% in substrate with stones. Of all the behavioral patterns, the one that stood out was the foraging, where 70.91% of individuals were foraging in the middle of the water column. Diet results reinforce the idea of the Astyanax species are omnivorous and opportunistic, where the specie fed the resources available in their environment showing high feeding plasticity along the stream. Species of the genus Astyanax are considered generalists in relation to habitat use and highly active, corroborating the results of this study.