Composição da dieta da raia de água doce Potamotrygon orbignyi (Castelnau, 1855) (Chondrichthyes: Potamotrygonidae) na região da ilha de Marajó - Pará

Abstract

South America is characterized by a wide diversity of freshwater fishes and among these species we can highlight the rays of the Potamotrygonidae family, whose representatives are restricted to the freshwater environment. Freshwater rays are distributed in several hydrographic basins of South America and are part of the chondrofauna of Marajó Island. The study of feeding ecology allows us to interpret the behavior, nutrition, and conservation of the species studied. The individuals (n = 24) were collected on Marajó Island, in the municipalities of Soure, Muaná, Afuá and Santa Cruz do Arari. Collections were done in several stages, covering dry and rainy periods between 2004 and 2006. Food items were identified down to the lowest possible taxonomic category. The analyses took into consideration qualitative and quantitative aspects, calculating the following indexes for each food item: Frequency of Occurrence (% FO), Percentage in Weight (% W), Numerical Percentage (% N), Index of Relative Importance (IRI) and respective percentage (% IRI). Observations were also made on the degrees of stomach filling and digestion of the items. The analyses pointed out that the item with the highest Frequency of Occurrence was material of plant origin (% FO = 85.71). The item with the highest Percentage in Number and Weight was the insect group (% N = 50.22 and % P = 50.30) including representatives of the orders: Orthoptera, Isopoda, Lepidoptera and Ephemeroptera. The percentage Relative Importance Index (% IRI) indicated a clear preference of this species for insects (% IRI = 57.44). The degree of. repletion of the analyzed stomachs indicated that they presented little content (45.83% with V4 repletion); while in relation to the degree of digestion, 29.11% of the analyzed items were highly digested (digestion degree 5). The results point P. orbignyi as an opportunistic predator species with a feeding preference for insects.