Eutrophication Indexes Used as Fish Production Parameters in the Itaipu Reservoir(Brazil)

The knowledge of liminology can be applied in studies of trophic state indexes and morfoedaphic indexes as factors for determining the inference fish production in reservoirs. This work is based on the hypothesis of the trophic cascade relations, particularly related to bottom-up and top-down effect in Itaipu Reservoir (Brazil). Using the data available by Itaipu, from 1999 to 2004, analyzes of multiple regressions were accomplished to determine the relationships of the dependent and independent variables. We applied the trophic state indices (TSI) based on readings Secchi disk, total phosphorus and chlorophyll-a density for obtaining TSI medium. Morfoedaphic index was calculated based on the reading of the concentration of dissolved solids and the inference of fishing yield, from this index. The average results of the trophic state indices indicate an oligotrophic status for the entire reservoir as well as for the riverine, transition and lacustrine zones separately. The fish was yieldn Estimated by the relation with cyanobacteria concentration, and this was the best variable que explained this prediction. The use of the morfoedaphic index (MEI), with the recorded catch data, predictive models can generate que estimate the fishing yield in the Itaipu Reservoir. The relations of MEI with chlorophyll-a and water transparency que Indicate this index may be a good predicting factor for future fish captures.

Bioactive extracts of red seaweeds Pterocladiella capillacea and Osmundaria obtusiloba(Floridophyceae:Rhodophyta) with antioxidant and bacterial agglutination potential

Objective:To evaluate the antioxidant,antibacterial and bacterial cell agglutination activities of the hexane(Hex) and 70%ethanol(70%EtOH) extracts of two species of red seaweeds Pterocladiella capillacea(P.capillacea) and Osmundaria obtusiloba.Methods:In vitro antioxidant activity was determined by DPPH radical scavenging assay,ferric-reducing antioxidant power assay,ferrous ion chelating assay,β-carotene bleaching assay and total phenolic content quantification.Antimicrobial activity was tested using the method of disc diffusion on Mueller-Hinton medium.The ability of algal extracts to agglutinate bacterial cells was also tested.Results:The 70%EtOH extract of the two algae showed the highest values of total phenolic content compared to the Hex extract.The results of DPPH for both extracts(Hex,70%EtOH) of Osmundaria obtusiloba(43.46%and 99.47%) were higher than those of P.capillacea(33.04%and 40.81%) at a concentration of 1 000 μg/mL.As for the ferrous ion chelating,there was an opposite behavior,extracts of P.capillacea had a higher activity.The extracts showed a low ferric-reducing antioxidant power,with optical density ranging from0.054 to 0.180.Antioxidant activities of all extracts evaluated for β-carotene bleaching were above 40%.There was no antibacterial activity against bacterial strains tested.However,the extracts of both species were able to agglutinate bacterial Gram positive cells of Staphylococcus aureus and Gram negative cells of Escherichia coli,multidrug-resistant Salmonella and Vibrio harveyi.Conclusions This is the first report of the interaction between these algal extracts,rich in natural compounds with antioxidant potential,and Gram positive and Gram negative bacterial cells.

Additional Records of the American Elephantfish <i>Callorhinchus callorynchus</i>(Chondrichthyes, Holocephali, Chimaeriformes) in Southeastern Brazil

Chimaeras, fish in the order Chimaeriformes, are among the rarest and least studied fish in the class Chondrichthyes (cartilaginous fish). Previous records have indicated that a species of chimaera known as the elephantfish, or cockfish, Callorhinchus callorynchus, may be found in marine waters off southeastern Brazil, as far north as the state of São Paulo. Here we report that C. callorynchus, caught with bottom gillnet, was found in an urban fish market in the city of Rio de Janeiro (~23˚S). This and other records from a variety of places call into question the distribution limits of the American elephantfish in the southwestern Atlantic Ocean and whether, at least seasonally, this species may often be found as far north as the state of Rio de Janeiro. Because of scientific and conservation interests in the poorly known Chimaeriformes, we recommend long-term monitoring of the fish catch in ports along the southern Brazilian coast, to better understand the natural history of the intriguing chimeras.

Historical Evolution of the Trophic and Limnological Relationships in the Itaipu Reservoir:Top-Down and Bottom-Up Effects upon Fish Production

Many experimental studies have contributed to the development of the theory of trophic chains in lacustrine habitats. They have revealed the important role played by fish, a subject that has been mostly ignored by limnological studies for the past few decades. Most of these studies were developed in Europe and in the United States. The general applicability of this theory has not yet been tested in subtropical and tropical habitats. In spite of controversies, the bottom-up: top-down trophic cascade hypotheses are the most adopted conceptual models. In this context, we examined if these hypotheses may be corroborated by data from the subtropical Itaipu Reservoir. A negative effect was verified between water transparency and total suspended solids. The detritivorous fish exerted a controlling effect on chlorophyll-a concentrations. Bottom-up effects were detected in four trophic levels, and top-down was detected in just one trophic level. The limnological variates influenced the chlorophyll-a concentration, which indicated that the lnTKN plus the effect of the quarter and the reservoir zone (and their interaction) were important.