Caracterização dos ovos e larvas de peixes na foz do rio Pará: plataforma continental norte do Brasil.

Abstract

Studies focusing on ichthyoplankton at Brazil’s northern coast are rare. Therefore, this study aims to characterize the specific composition and distribution of the ichthyoplankton in the Continental Platform of Northern Brazil. We analyzed and quantified the relative abundance of organisms, their frequency of occurrence, density and distribution in the area of interest. Gathering of samples occurred in October 2014 and January 2015 as part of the INCT AmbTropic Pará River project, located at the Continental Amazonian Platform. Collection of samples was performed in six to seven longitudinal stations relative to the coast throughout a transection in the Continental Platform in Northern Brazil. Transportation to the area of interest was by a boat adapted for research. The seine net used for collection of plankton was Bongô type, the diameter of its main opening was 60 cm and the mesh diameter was 500 μm for trapping of biological material. The volume of water filtered through the net was measured using a fluxometer. Oblique net dragging was performed throughout the water body. Collected samples were fixed in 4% formaldehyde followed by quenching with sodium tetraborate (Borax) and placed in properly labeled polyethylene tubes. The ichthyoplankton were screened in the laboratory and species were classified and analyzed to the most specific taxonomic level identifiable. From samples collected in October 2014, during drought, the highest density of individuals was found at station 01 (349.01 individuals in 100m3), which was the most coastal station. The lowest density was found in station 03 (7.0 individuals in 100m3). When quantifying eggs, the highest density occurred in station 05 (33.4 eggs in 100m3) and the lowest at station 06 (1.3 eggs in 100m3). A total of 110 eggs and 297 larva were counted belonging to 23 families, 22 genus and 26 species. The highest occurring families were Carangidae (66.66%), Gobiidae (66.66%) Scombridae (66.66%) and Sciaenidae (50%). While measuring relative abundance, the Engraulidae family stood out, achieving highest representation in the coastal stations. However, egg abundance was higher in non-coastal stations. The collection performed in January 2015, during rainy season, had highest density of larva in station 02, most coastal, (248.7 individuals in 100m3), and lowest density in station 06 (9.46 individuals in 100m3). In the same collection, the highest egg density (133.47 individuals in 100m3) and relative abundance was found in station 03. Highest relative abundance of eggs was also found at station 03, while station 07 measured the lowest egg abundance. Overall, through the January collection, 230 eggs and 1,682 larva were counted, distributed in 27 families, 37 genus and 40 species. The most represented families were Carangidae (71.42%), Ophichthidae (71.42%), Gobiidae (57.14%), Haemulidae (57.14%), Paralichthyidae (57.14%) and Scaridae (57.14%). While measuring relative abundance, the most families Gobiidae and Eleotridae achieved highest representation.