Cristina Cox Fernandes

Research Interests: 

Diversity of Amazonian Fishes

My work focuses on the ecology and evolutionary diversity of neotropical freshwater fishes, particularly within the Amazon River basin. Neotropical fishes make up a significant percentage of the world freshwater icthyofauna, with new species being described at an impressvie rate. Much of my research aims to provide basic information about these fishes, from behavior and ecology, to taxonomy and sexual dimorphism, especially within the Gymnotiformes (electric fishes).

A hallmark feature of Amazonian fish is that they adapt to extreme seasonal changes in habitat properties such as water level, oxygen availability, and space. I have a long-standing interest in one such adaptation--lateral migration--in which fishes swim away from floodplains when conditions are poor and return when conditions improve. This appears to be a basic and widespread adaptation, occurring in at least 20 Amazonian species. In my studies of lateral migration I have used various approaches including direct observations and capture of migrating fishes, interviews with subsistence and commercial fisherman, assessment of habitat quality, and evaluation of fish physiological and reproductive condition. One of the significant results from my work concerns intrapopulation variation in behavior; I have found that some individuals of a population engage in a reproductive migration, returning immediately to the same floodplain area, while other individuals migrate in what appears to be a dispersal event. This work raises additional questions that I would like to pursue, such as: What factors trigger lateral and longitudinal (upstream and downstream) migrations in Amazonian fishes? Do lateral migrations initiate longitudinal migrations? How do fishes choose a floodplain habitat at the end of their longitudinal migrations? What are the effects of dispersion migrations on gene flow within these species?

My work also examines the large-scale ecology and distribution of benthic fishes across the Amazon basin. Since 1992 I have been involved in a project entitled 'Fish Diversity of the Principal Channels of the Amazon River' (Calhamazon), funded by the National Science Foundation and Brazilís Conselho Nacional de Pesquisas. In this project, our group (headed by John G. Lundberg) trawled sections of the main Amazon river channel (about 3,500 km) including in the lower reaches of the Amazonís major tributaries. We are documenting a remarkable abundance and diversity of fishes, over 360 species, most of which are catfishes and electric fishes, and several of which are new to science. This project has provided an immense data set for the quantitative study of the community ecology of these fishes. One of my findings is that distribution, diversity and community structure of the 43 electric fish species in these rivers are strongly influenced by the location of tributaries, and by the physiochemical features of the water. For instance, we have found that tributaries enrich the species diversity and composition of Amazon mainstem electric fish communities, particularly in the westernmost white water tributaries. The diversity appears to increase immediately downstream of tributaries. Also, we have found that some families of electric fish, such as the Apteronotidae, are particularly abundant in 'white' waters, while others, such as the Sternopygidae, are most abundant in 'clear' and 'black' waters. I plan to assess the community structure of other benthic fish groups as well in the near future.

Another part of my present work examines the taxonomy of Gymnotiformes (electric fish), a group that comprises over 100 species. My interest in the taxonomy of this group was initially geared towards species identification, for my work on community ecology. As part of my training I have visited all of the electric fish collections in the United States and Brazil, and have been regularly collecting new specimens in central AmazÙnia. With colleagues I have recently described a new genus of electric fish with two species. I have also discovered a pronounced morphological sexual dimorphism in several species in the family Apteronotidae, the most diverse family of Gymnotiformes. Males of these species exhibit unusually long snouts, which had led them to be classified initially in genera separate from the females. I discovered this dimorphism while examining the gonads of museum specimens, when I realized that all of the hypermorphic individuals were male. Another case of a taxonomic error resulting from sexual dimorphism occurred in the genus Oedegmognathus, in which fishes with teeth outside of their mouths had been initially classified in one genus, whereas individuals without this character had been classified erroneously as part of another genus. Fishes with teeth outside of their mouths turn out to all be males. Another species in the Apteronotidae family was recently studied by a colleague (Eric Hilton) and I, for which we have described the osteological bases for sexual dimorphism.