Spatial and temporal variation of fish assemblage associated with aquatic macrophyte patches in the littoral zone of the Ayapel Swamp Complex, Colombia

ABSTRACT: Aim: The purpose of the present study was to examine spatial and temporal variation in fish assemblage structure associated with aquatic macrophytes in the littoral zone of the ASC. Methods: Specimens were caught between January 2008 and February 2009, over four limnimetric moments, using both cast net and seine net. Data on the temperature, electrical conductivity, pH and dissolved oxygen was recorded for the characterization of the water mass in the sites. Results: A total of 34,151 specimens from 44 species were collected. The most abundant species were Eigenmannia virescens, Astyanax caucanus, Astyanax fasciatus, Roeboides dayi and Cyphocharax magdalenae, which together accounted for more than 75% of the sample. Temporal and spatial comparisons showed variation in the environmental conditions and highlighted the existence of heterogeneous abiotic conditions (p0.05) regarding the fish assemblage structure. The multivariate analysis showed no significant relationship between existing environmental conditions and the fish assemblage (p=0.04). The analysis also showed the absence of a relationship between the fish assemblage and environmental variables with respect to the flood pulse and sampling sites (p>0.05). Conclusion: The uniformity of the fish communities that inhabit aquatic macrophyte patches in the littoral region of the ASC may be related to the availability of suitable habitat in structural terms, that probably supports a more abundant and varied wildlife

Hydroacoustic evaluation of the spatial and temporal distribution of fish in the upstream proximity of a dam in a Neotropical reservoir

Background. Construction of dams alters the physical, chemical, and ecological characteristics of the aquatic environment and modifies fish behaviour and the community composition. Few studies have shown the diel and seasonal fish distribution in tropical reservoirs, mainly in the proximity of the dam, where the risk of injury and death of fishes, which try to migrate downstream, is high. Thus, the data obtained in these regions can encourage actions that may attenuate the impacts on ichthyofauna. Hydroacoustic sampling is an effective tool to study fish behaviour and their spatial distribution in water bodies. In this context, the aim of this study was to evaluate the spatial and seasonal distribution of fish in the reservoir of Três Marias (Minas Gerais, Brazil), immediately upstream of the dam, using hydroacoustic and gillnet sampling. Materials and methods. Hydroacoustics and gillnet sampling were carried out both during the day and at night, and during the rainy and dry seasons. For the acquisition of hydroacoustic data, we employed an echosounder (BioSonics DT-X Digital Scientific) with a split-beam digital transducer. For the biological data, gillnets of different mesh sizes were set. Results. Hydroacoustic data showed significant differences in fish depth between day and night surveys, with fish remaining in deeper water during the day, a phenomenon known as Diel Vertical Migration. Furthermore, hydroacoustic data showed that smaller fish (estimated by “target strength”) concentrate at smaller depths. There was no significant difference in the size of fish between seasons. Limnological and operation variables were not related to the fish  abundance. Distribution maps showed that during the day fishes were distributed in areas more distant from the dam, while at night they were closer to the dam. Gillnets sampled 127 individuals of 22 species and 57.5% of the collected specimens were migratory species. Conclusion. These results can contribute to the understanding of fish behaviour in reservoirs, as well as provide an empirical basis for the development of novel fish management measures for Neotropical dams

Avaliação de frações da matéria orgânica do solo para caracterização de áreas degradadas

A quantificação e o fracionamento da matéria orgânica do solo em carbono solúvel, carbono solúvel em solução salina e matéria orgânica leve podem ser usados como ferramentas para caracterizar a recuperação de áreas degradadas. Para este fim, coletaram-se amostras de solos em talude, submetidos à recuperação em novembro de 1994 com vários tipos de cobertura vegetal, no município de Viçosa. Os tratamentos corresponderam a: solo sem vegetação, solo em recuperação com predomínio de leguminosas, solo revegetado com maior presença de gramíneas, solo sob pastagem natural e solo sob floresta. Os resultados mostraram que o fracionamento do carbono orgânico do solo em carbono solúvel em solução salina, matéria orgânica leve e carbono solúvel em água auxilia na caracterização de áreas degradadas. O carbono solúvel em solução salina foi o procedimento mais sensível para caracterizar áreas degradadas a partir de diferentes coberturas vegetais