Length-weight relationship for seven freshwater fish species from Brazil

The present study reports length-weight relationships for seven native freshwater fish species (Triportheus angulatus, Psectrogaster rhomboides, Prochilodus brevis, Leporinus piau, Cichlasoma orientale, Crenicichla menezesi, and Pimelodella gracilis) captured in a semiarid Brazilian reservoir located in the state of Rio Grande do Norte.

Aggressiveness Overcomes Body-Size Effects in Fights Staged between Invasive and Native Fish Species with Overlapping Niches

Approximately 50 years ago, Nile tilapia were accidentally introduced to Brazil, and the decline of pearl cichlid populations, which has been intensified by habitat degradation, in some locations has been associated with the presence of Nile tilapia. There is, however, little strong empirical evidence for the negative interaction of non-native fish populations with native fish populations; such evidence would indicate a potential behavioural mechanism that could cause the population of the native fish to decline. In this study, we show that in fights staged between pairs of Nile tilapia and pearl cichlids of differing body size, the Nile tilapia were more aggressive than the pearl cichlid. Because this effect prevailed over body-size effects, the pearl cichlids were at a disadvantage. The niche overlap between the Nile tilapia and the pearl cichlid in nature, and the competitive advantage shown by the Nile tilapia in this study potentially represent one of several possible results of the negative interactions imposed by an invasive species. These negative effects may reduce population viability of the native species and cause competitive exclusion.

Are biological species and higher-ranking categories real? Fish folk taxonomy on Brazil`s Atlantic Forest coast and in the Amazon

Analysis of Brazilian fishers` classifications of 24 marine (Atlantic coast) and 24 freshwater (Amazon) fish species reveals that fishers from the Atlantic coast identify fish mainly through generic names (primary lexemes), while riverine Amazonian fishers typically identify them through binomials. The similarity of Amazonian fish species seems to contribute to the detailed folk taxonomy used by riverine fishers. High-ranking groups called ""relatives"" or ""cousins"" are sorted by fishers in terms of similarities of habitat, diet, and morphology and, secondarily, behavior. The general correspondence between the folk and scientific taxonomies reinforces the reality of both the supracategories used by these fishers and the biological groups as discontinuities in nature. Given the urgency of biological inventories and the lack of knowledge of high-biodiversity environments such as the Atlantic Forest and the Amazon, these results suggest that fisher knowledge and experience could contribute to scientific research.

Knodus dorsomaculatus (Characiformes: Characidae), a new species from Teles Pires River, Tapajos River basin, Brazil

Knodus dorsomaculatus, a new species, is described from Teles Pires River, a tributary of the Tapajos River, Brazil. It can be distinguished from its congeners by the presence of a conspicuous dark blotch on the base of the first five branched dorsal fin rays and the presence of ii,9 dorsal fin rays. Additional comparisons between K. dorsomaculatus and its congeners are presented.

Mercury and Nitrogen Isotope in a Marine Species from a Tropical Coastal Food Web

The present study raised the hypothesis that the trophic status in a tropical coastal food web from southeastern Brazil can be measured by the relation between total mercury (THg) and nitrogen isotope (delta(15)N) in their components. The analysed species were grouped into six trophic positions: primary producer (phytoplankton), primary consumer (zooplankton), consumer 1 (omnivore shrimp), consumer 2 (pelagic carnivores represented by squid and fish species), consumer 3 (demersal carnivores represented by fish species) and consumer 4 (pelagic-demersal top carnivore represented by the fish Trichiurus lepturus). The values of THg, delta(15)N, and trophic level (TLv) increased significantly from primary producer toward top carnivore. Our data regarding trophic magnification (6.84) and biomagnification powers (0.25 for delta(15)N and 0.83 for TLv) indicated that Hg biomagnification throughout trophic positions is high in this tropical food web, which could be primarily related to the quality of the local water.

Effects of exposition to polluted environments on blood cells of the fish Prochilodus lineatus

In this study, we investigated the effects of contaminated water on the blood parameters of the fish Prochilodus lineatus exposed during 7 and 20 days. Blood was collected with heparinized syringes, and blood smears were prepared and stained with Leishman stain. Slides were examined and photographed using a Leica light microscope. Total white blood cell counts and differential counts of thrombocytes and leukocytes were obtained for statistical analysis. The group exposed to water samples from Lago Azul exhibited an increase in the number of leukocytes and in the total number of white blood cells, suggesting that the chemical contaminants in this environment were acting similarly to antigens in this fish species, causing the proliferation of defense cells. In the group exposed to detergent during 20 days, the number of thrombocytes decreased. These results suggest that the variations in the number of leukocytes were indicators of environmental pollution and that biodegradable detergents may, after a certain time of exposure, affect vital functions in fish, such as coagulation and prevention of infections, which directly involves thrombocytes. Microsc. Res. Tech., 2012. (c) 2011 Wiley Periodicals, Inc.

Predation on microcrustaceans in evidence: the role of chaoborid larvae and fish in two shallow and small Neotropical reservoirs

This study was focused on the predation upon microcrustaceans by an invertebrate predator (chaoborid larvae), and vertebrate predators (fish), in two small reservoirs in southeastern Brazil, with and without macrophytes, in two climatic periods (dry and rainy seasons). Chaoborus larvae were sampled in the limnetic zone, as they are scarce in the littoral, and fish in both limnetic and littoral zones. Their diets were evaluated by the analysis of the crop (chaoborid) or stomach contents (fish). Chaoborid larvae consumed the dinoflagellate Peridinium sp. or other algae, rotifers, and planktonic microcrustaceans. The fish species that included microcrustaceans in their diets were juveniles caught in the littoral. Aquatic insects, plant fragments, and detritus were their major dietary items, microcrustaceans representing a minor item. Planktonic copepods contributed more to the diet of chaoborid larvae than planktonic cladocerans. Fish preyed on planktonic microcrustaceans, as well as on benthic and macrophyte-associated species. Microcrustaceans were not heavily preyed on by chaoborid larvae and fish in both reservoirs.