Trophic ecology of Hemigrammus marginatus Ellis, 1911 (Characiformes, Characidae) in a conserved tropical stream.

The trophic ecology of ichthyofauna in a stream can be related to the presence or absence of riparian and aquatic vegetation, and mainly resource availability. Therefore, the aim of this study was to analyse the seasonal and ontogenetic variations for the trophic ecology of Hemigrammus marginatus in the Beija-Flor stream located at the Jataí Ecological Station in the municipality of Luiz Antônio-SP, Brazil. In order to attain this objective, the data collections were carried out on a monthly basis from August, 2011 to July, 2012. Fish were collected using a trawl net and bait traps from three collection stations distributed along the Beija-Flor stream. The quality of the water was evaluated by the chemical variables: ammonia, nitrate, total nitrogen, total phosphorus, and physical temperature, dissolved oxygen, pH, turbidity and conductivity, obtained by using a Yellow Springs sonde. The collected specimens were fixed in 10% formalin in the field and were subjected to biometric measurements in the laboratory. The stomachs were weighed and transferred to 70% alcohol and the stomach contents were analysed using a stereomicroscope at the lowest possible taxonomic level. The species was considered insectivorous and the autochthonous food items were the most important during the dry season, mainly from the orders Ephemeroptera and Trichoptera, while allochthonous items from the order Hymenoptera were more important in the wet season. The young individuals' diet was based on the consumption of zooplankton, and insofar as the fish develops, there was a decrease in this item in the diet showing that the species has ontogenetic shifts in its diet. The conservation state of the Beija-Flor stream, as well as the flexibility of using food and food resources provided by aquatic macrophytes and riparian vegetation are key factors for the high abundance of the H. marginatus species.