Dinâmica Sazonal, Espacial e Dieta De Larvas De Siluriformes Bentônicos Do Médio Rio Amazonas – Brasil

Abstract

CHAPTER 1: Studies carried out in Amazonian rivers show that some species of Pimelodidae catfish use the river channel as a nursery and also as a growing site. Even though we know a great deal about the dynamics of fish larvae from Amazonian systems, there is still a lack of knowledge about the determinants of abundance, diversity and dynamics of the larval assembly that develop in the deeper parts of the rivers of this region. The objective of this work was to determine the spatial and temporal dynamics of benthic Siluriformes larvae that develop in the channel of middle Amazon river. Sampling of benthic Siluriformes larvae were conducted quarterly with benthic trawl net at eight previously selected sites covering 100 km of the middle Amazon River. A total of 576 benthic trawls were conducted, capturing 6731 larvae of Siluriformes, distributed in 36 species. The Pimelodidae family was the most abundant with 94.25% of the total individuals and represented by 26 taxa. Hypophthalmus marginatus was the most abundant species, both in the hydrometric periods as well as and in the evaluated depths. Species of commercial importance such as those belonging to the genus Brachyplatystoma were also found in this study. The results revealed that the larvae were present during flood, full, ebb and dry period, however, the composition and abundance were significantly different in the hydrometric periods and different depths. The physico-chemical variables, such as temperature, pH, oxygen, conductivity and turbidity did not have a significant influence on the abundance and composition of Siluriformes larvae, but, in this case, hydrometric period is the factor that influenced the dynamics of the same. This study demonstrates that flood pulse is the factor that influences the dynamics of larvae of benthic systems middle Amazon River. Moreover, this research showed that the river channel serves as a growth and shelter site for Siluriform larvae, regardless of spatial and seasonal changes. CHAPTER: 2 The acquisition, digestion and assimilation of food is fundamental to the growth and survival of fish larvae in systems aquatics, especially when they are in development ontogenetic.The objective of this study was to analyze the diet and trophic structure of benthic Siluriformes larvae in the medium Amazon River, and to verify possible seasonal and spatial changes. A total of 1074 stomach contents belonging to 36 species were analyzed, and the food index (IAi) was calculated for each one. Based on the predominant food item consumed in the diet, most of the species were zooplanktonic, with cladocerans being the most consumed food item. Aquatic insects were the second most important item in the diet of the species, where Diptera larvae, specifically Chironomidae and Chaoboridae, are the most important items. Microcrustaceans were consumed at all periods and at all evaluated depths, except in the flood period where microcrustaceans and aquatic insects were consumed in almost equal proportions. Regarding the origin of food, the larvae used almost exclusively native resources, microcrustaceans and aquatic insects being the major representatives. Even if, other foods were available in the environment, Siluriformes larvae showed positive selection by microcrustaceans. The trophic structure showed seasonal and spatial variations, being influenced by the flood pulse. It is concluded that the benthic system is productive enough for the maintenance of Siluriform larvae in the channel of large rivers, by incorporating resources from floodplain areas or even by the direct production of the benthic system.