Influência temporal e ontogenética na dieta de um caracídeo na dolina cárstica Lagoa Misteriosa - MS, Brasil

Abstract

Knowledge about the environmental and biological factors that influence variations in the diet of fish species is essential for understanding the ecological processes at work among the populations and their relationships with the environment. However, relatively little of this information is available for fishes present in lakes formed by flooded karst dolines in the Neotropical region. This study sought to determine the diet of Deuterodon luetkenii in the karstic dolina Lagoa Misteriosa, southwestern Mato Grosso do Sul State, the deepest flooded cave in Brazil, deeper than 220 meters deep. It was also checked whether the feeding composition of the species varies temporally and ontogenetically. Sampling was carried out on a bimonthly basis at three points on the banks of the lagoon on two occasions throughout the year (With Algae Blooms =WAB and Absence of Algae Blooms = AAB). The food items were analyzed according to the volumetric and occurrence frequency methods and the diet was characterized by the Food Index (IAi%). To determine ontogeny, the specimens were divided into four size classes. Deuterodon luetkenii showed a herbivorous diet by consuming basically macrophyte fragments and filamentous algae. Although these food items were the most ingested by the species in both periods, there was a significant difference in diet between the sampled periods. In the AAB period, the species' diet was practically based on fragments of macrophytes and filamentous algae, while in the WAB saw a decrease in the intake of these items and an increase in the consumption of aquatic invertebrates. Ontogenetically, the species showed a significant difference in diet between size classes, however without correlation between periods and classes. Smaller individuals mainly consume filamentous algae and, the larger the size class, the lower the consumption of this item, being replaced by fragments of macrophytes. The results found reinforce the importance of resources of autochthonous origin in the food composition of the species and the influence of aquatic plants for this lake ecosystem with unique characteristics. The findings also point out to the need for the pursuit of more complex ontogenetic studies between morphological, behavioral, and ecological characteristics of fish species.