Longitudinal and ontogenetic changes in feeding patterns of an insectivorous Crenuchidae in streams of southern Brazil

The genus Characidium has the highest species richness within the Crenuchidae family and the Characidiinae subfamily. Characidium pterostictum holds immense importance due to its widespread distribution in South America, especially in the hydrographic systems of the Uruguay River. The objective of this study is to describe the feeding biology of Characidium pterostictum in streams of the Ijuí River basin (Uruguay River system) in southern Brazil and to identify potential spatial and ontogenetic variations in its diet. Samples were collected from three tributaries of the Ijuí River. Food items were identified and quantified using the volumetric method and frequency of occurrence. Characidium terostictum was characterized as an insectivorous fish, a specialization previously reported in Characidiinae. There was a slight difference in feeding patterns based on variations in standard length and sampling sites. Ontogenetic analysis showed that C. pterostictum expands its feeding spectrum as it develops. The consumption of autochthonous items such as insect remains (Ephemeroptera, Trichoptera, and Chironomidae) as the primary component of diet indicates that this fish species requires extensive preservation of the watercourses it inhabits.