Nicho trófi co de Orestias agassii (Cuvier & Valenciennes, 1846) del sistema de arroyos del salar de Huasco (20°05'S; 68°15'W) Trophic niche of Orestias agassii (Cuvier and Valenciennes, 1846) in the streams system of salar de Huasco (20°05'S; 68°15'W)

The absence of biological and ecological information on native fi shes at the isolated hydrological systems of the Chilean southern Altiplano is one of the main concerns for current research in this fi eld. This fact is even more evident when considering the environmental deterioration of this region due to negative water balance and the demand of water by mining which have accelerated eutrophication processes and increased salinity. Therefore, it is important to obtain detailed information about the fi sh fauna in the Altiplano area. Based on this, the trophic aspects O. agassii were studied during two climatic periods (autumn and spring) at the stream system of the Huasco salt pan. Using the numerical importance index (IIN), the Manly and Chesson selectivity index and the estimation of the niche amplitude, the feeding habits of 51 specimens were analyzed. The stomach content analysis showed differences between prey items consumed for each period. The most representative groups for each sampling corresponded to Class Cladocera and Ostracoda, with 52.1% and 45.4% respectively. For both males and females, the most important prey (IIN) for spring was Ostracoda. During autumn, the highest value item for IIN for males was Cladocera Alonella and, for females the item Ostracoda. According to the selectivity analysis, O. agassii presents a marked preference for larvae of the Family Ephydridae, ostracods and the Cladocera Alonella and it also exhibits stenophagic feeding that would coincide with the marked selectivity for a low number of taxa compared to the environmental offer.