Aplicação da Análise de Fourier Elíptica no estudo da forma do corpo dos peixes marinhos demersais do Nordeste do Brasil

Abstract

Morphology refers to the study of the form of living organisms, and shape are the geometric properties that do not vary with changes in position, rotation, and size of individuals. Functional morphology is the branch of science that studies the relationships between morphological characters and environmental, physical and biological factors. The contour is a representation of the shape in two dimensions, and one of the methods that can be used to describe the shape of this structure is the Elliptic Fourier Analysis (EFA). In EFA, the contour is represented by independent parametric functions of the coordinates x and y, configured as cumulative functions of a third variable t along the boundary. Based on this method, the aim of this study was to evaluate the functional morphology of the demersal marine fishes of the continental shelf of Northeast Brazil, and to identify which morphological aspects of the fish body allow the connectivity between the types of bottom environments in the study area. Fish were collected using a bottom trawl between latitudes 4-9°S. During the collection the type of bottom were also observed for each sampling station. For each individual the body contour was obtained (removing the fins and tail) in x and y coordinates. The data were analyzed in software R. We applied the EFA, principal component analysis and cluster analysis to understand the functionality of the fish through the shape. The results concluded that the EFA showed to be efficient in the morphological study of the fish shape, and 10 groups were determined based on body shape. The functional aspects of the body shape are regarded to swimming performance, that is, more elongated shapes are associated with higher swimming speeds, and high bodied shapes are associated with maneuverability. The type of habitat bottons were directly related to the shape of the individual. Fishes living in the open (sand bottom) need a more elongated and aerodynamic bodies due to physical factors of the environment, such as velocity of the stream. The structured environment (SWCR - sand with corals and rocks) favors extreme shapes, for example, extremely elongated body (trumpet-fish) or deep and high body (e.g. Chaetodontidae family). Medium-elongated shapes were the most representaive among the demersal fishes analyzed; they were related to a greater diversity of species and connectivity between the types habitats that compose the continental shelf of northeastern Brazil.