Karyotype variability in eight species of the subfamilies Loricariinae and Ancistrinae (Teleostei, Siluriformes, Loricariidae)

Loricariidae is one of the largest fish families of the world, with about 650 species separated into six subfamilies. To date, cytogenetic data on only 56 species of this family are available. In the present study, the karyotypes of three Ancistrinae species and five Loricariinae species were studied. The lowest diploid number, 2n=38, was observed in Ancistrus n.sp. 1 (Ancistrinae) and the highest diploid number, 2n=70, was observed in Rineloricaria n.sp. (Loricariinae). The nucleolar organizer regions (NORs) were seen at a terminal position in six species and at an interstitial position in two. The karyotypic analysis of Loricariinae and Ancistrinae species revealed that these groups exhibit a large diversity of diploid numbers, suggesting the occurrence of intense karyotypic evolution during their evolutionary history.

Composição e abundância da ictiofauna na zona litorânea de um tributário, na zona de sua desembocadura no reservatório de Jurumirim, Estado de São Paulo, Brasil

Monthly collections of fishes using a trawl net were carried out from August 1996 to December 1997 with the objective of evaluating the composition and diversity of fish species in the littoral area of the transition zone between Veados Stream and Jurumirim Dam (Upper Paranapanema River, São Paulo State). Diversity and similarity indices of ichthyofauna at the sites were determined and correlated with abiotic factors such as dissolved oxygen, temperature, pluviometric precipitation and hydrological level. Twenty-six (26) fish species (the majority small-sized) of the family Characidae (Tetragonopterinae and Cheirodontinae) were registered. Representatives of the orders Siluformes, Gymnotiformes, Perciformes and Synbranchiformes occurred in lower abundance. Significant differences were found in the site diversity indices, but not in the abiotic factors. Significant correlations between the abundance of the ichthyofauna and the variations in the abiotic factors were not detected. The presence of fish larvae in the samples indicates the importance of the transition zone as a reproduction area of the fish species registered in this study.

First cytogenetic description of the species Rhamdella microcephala (Pisces, Hepapteridae)

Cytogenetic studies were carried out on Rhamdella microcephala collected from the headwaters of the Machado river, a tributary of the Sapucaí river, Minas Gerais, Brazil. Sixteen specimens exhibited 2n=56 chromosomes, with 18 metacentrics, 30 submetacentrics and 8 subtelocentric-acrocentrics (FN=84). The nucleolar organizing regions (NORs) were identified in the interstitial position on the long arm of a submetacentric pair (pair 12). Chromomycin A3 staining evidenced only the NOR-bearing segments. Positive C-band segments were identified in a pericentromeric position in most of the chromosomes and the NOR-bearing segments were also C-band positive. Some aspects related to the chromosomal characteristics of Rhamdella microcephala are discussed.

Characterization of bornite (Cu5FeS4) electrodes in the presence of the bacterium Acidithiobacillus ferrooxidans

Bornite electrodes were characterized in the absence or in the presence of Acidithiobacillus ferrooxidans, which is an important microorganism involved in metal bioleaching processes. The presence of the bacterium modified the mineral/electrolyte interface, increasing the corrosion rate, as revealed by interferometric, AEM, ICP and EIS analyses. As a consequence of bacterial activity the electrode became porous, increasing its surface heterogeneity. This behavior was correlated with the evolution of impedance diagrams obtained during the time course of experiments. The main difference in these diagrams was the presence of an inductive feature (up to 44 h), which was related to bacterial action on the mineral dissolution, better than to its adhesion on the bornite. The total real impedance measured in presence of the bacterium was about 10 times lower than in its absence, due to the acceleration of the mineral dissolution, because an oxidant environment was maintained.

Chromosome localization of the ribosomal genes 18S and 5S in four stocks of rainbow trout (Oncorhynchus mykiss) from cultivated and naturalized stocks in Brazil

In the present study, fluorescence in situ hybridization (FISH) was employed to determine the chromosomal location of genes 18S rDNA and 5S rDNA in four rainbow trout stocks. In specimens from the stocks of Núcleo Experimental de Salmonicultura de Campos do Jordão and Gavião river, 18S genes were located at a subterminal position in the long arms of two submetacentric chromosomes, whereas in specimens from stocks of Mount Shasta and Teresópolis they were found in the short arms. In all analyzed stocks, 5S genes were located in two chromosome pairs. In a subtelocentric pair, 5S genes were present in the short arms and, in the other submetacentric pair, 5S genes were at an interstitial position. In the latter, 18S and 5S genes were contiguous. Taking into account that both 18S and 5S rDNA genes have been localized in the short arm of a submetacentric chromosome in almost all rainbow trout samples so far studied, the presence of such genes in the long arm, as seen in the samples from Núcleo Experimental de Salmonicultura de Campos do Jordão and Gavião river, supports the hypothesis of a pericentric inversion involving this chromosome segment in the ancestor line of these stocks. The observed polymorphism allowed the identification of a very useful genomic marker, and may therefore constitute an important tool in the genetic management of rainbow trout stocks.

Cytogenetic analysis of A-, B-chromosomes and ZZ/ZW sex chromosomes of Characidium gomesi (Teleostei, Characiformes, Crenuchidae)

Different cytogenetic techniques were used to analyze the chromosomes of Characidium gomesi with the main objective of comparing the base composition of ZZ/ZW sex-chromosomes, B-chromosomes and the heterochromatin of A-chromosomes. The results of digestion of chromosomes with AluI restriction endonuclease (RE), silver and CMA3 staining, C-banding and fluorescence in situ hybridization (FISH) with the 18S rDNA probe suggested the existence of compositional differences between the heterochromatin of ZZ/ZW sex-chromosomes, A- and B-chromosomes, and indicated the presence of different numbers and morphology of B-chromosomes in the samples of this population.

Cytogenetic analyses of Pseudopimelodus mangurus (Teleostei: Siluriformes: Pseudopimelodidae)

The cytogenetic analyses showed that Pseudopimelodns mangurus has a diploid number of 2n=54 chromosomes (6M, 26SM, 12ST and 10A), single Ag-NORs on the short arm of a middle-sized ST pair, identified as pair 19, and a very small amount of C-band positive segments in two chromosome pairs. The Ag-NORs are C-band positive. The staining of the chromosomes of P. mangurus with CMA 3 reveled the occurrence of bright signals corresponding to the Ag-NORs segments, to the C-band positive segments and also to some C-band negative segments. The occurrence of a diploid number of 2n=54 in all species of the family Pseudopimelodidae and its absence among representatives of Pimelodidae and Heptapteridae, two related families previously considered, reinforces the hypothesis that Pseudopimelodidae is a monophyletic group. © 2004 The Japan Mendel Society.

Genetic conservation of Brazilian fishes - Present state and perspectives

Natural environments have been worldwide affected by the growing impact of anthropogenic actions that promote the reduction or the extinction of several vertebrate species. Aquatic ecosystems represent one of the most affected environments and many fish species and/or populations have been increasingly fragmented distributed due to habitat degradation, predatory fishing, introduction of exotic species, river sedimentation, deforestation, pollution, reduction of food resource, and construction of hydroelectric dams. Actually, more than 150 Brazilian fish species, including freshwater, estuary and coastal species, can be considered threatened. Information on the diversity, conservation biology and population analysis on threatened species or populations, with several DNA markers, can be extremely useful for the success of fish species-recovery and maintenance programs. Although DNA analysis in Neotropical fish species are just beginning, they tend to increase with the widespread attention to the use of molecular approaches to minimize problems related to the risk of extinction. The accumulation of information on biology and pattern of genetic variation of fish species, associated with ecological and demographic data, and also education and respect to the nature, constitutes a crucial task to develop efficient conservation strategies in order to preserve the genetic diversity in aquatic environments.

First chromosome characterization in the neotropical eel, Gymnothorax ocellatus (Pisces, Muraenidae)

Cytogenetics studies in 12 specimens of Gymnothorax ocellatus reveled a diploid chromosome number of 2n=42 (16 metacentrics, 18 submetacentrics and 8 acrocentrics). The nucleolar organizer regions were located in a terminal position on the long arm of the chromosome pair number fifteen. Conspicuous blocks of constitutive heterochromatin were observed in the centromeric and pericentromeric regions of some chromosome pairs. The results obtained are similar to those previously described for others species of this family. However, the cytogenetic informations may be useful in the identification of a possible variety of this species in Brazilian coast and contribute to the understanding of relationships among the species and the process of diversification which occurred in this group. © 2005 The Japan Mendel Society.

Comparative cytogenetic studies in species of the subfamily Callichthyinae (Teleostei: Siluriformes: Callichthyidae)

In the present study, the karyotype of three species (nine populations) of the Callichthyinae subfamily were investigated with the objective of better understanding the pattern of relationship among the genera that compose the subfamily. Among the four populations of Callichthys callichthys studied, two showed 2n=56 chromosomes and two 2n=58 chromosomes. Up to eight additional microchromosomes were observed in the sample from Marilia. The three populations of Hoplosternum littorale displayed the same number of chromosomes, 2n=60, and karyotypic constitution, 6M+2SM+52A. The two populations of Megalechis personata showed 2n=62 chromosomes and similar karyotypic formulae, 8M+54A and 6M+2SM+54A. Terminal Ag-NORs were found in one chromosome pair of C. callichthys, H. littorale, and M. personata from Itiquira, and in two pairs in M. personata from Rio Branco. The populations of C. callichthys showed C-band positive segments in centromeric and pericentromeric position and the populations of H. littorale and M. personata exhibited C-band positive segments in centromeric and/or interstitial position. Contrarily to the extensive chromosome rearrangements verified in the Corydoradinae subfamily, in the Callichthyinae subfamily a small number of changes seems to have occurred in its karyotypic evolution.

Comparative cytogenetics of nine species of Hypoptopomatinae (Teleostei: Siluriformes: Loricariidae): The importance of structural rearrangements in chromosome evolution

Fishes of the subfamily Hypoptopomatinae are very common and found in the lowlands of cis-Andean South America from Venezuela to the north of Argentina. With the main objective of contributing for a better understanding of the importance of chromosome rearrangements in the loricariid evolution, cytogenetic analyses were conducted in nine species of Hypoptopomatinae. The results showed a marked gross karyotypic conservation with the presence of 2n=54 chromosomes in all species analyzed. The main differences were found in the karyotypic formulae level. Most species had a single interstitial Ag-NORs, however terminal Ag-NORs were observed in three species. One species exhibited two Ag-NOR-bearing chromosome pairs. The distribution of C-band positive segments was species specific but chromosome markers were observed among the species analyzed. The gross cytogenetic characteristics observed among the Hypoptopomatinae species are similar to those observed in other primitive Loricariidae species suggesting that small changes, mainly paracentric and pericentric inversion were the main events in the karyotypic evolution of this fish group.

Prediction of voltage over electrodes' filaments of fluorescent lamps during dimming operation

This paper presents an investigation concerning the use of fundamental approximation analysis and a new lamp model for the prediction of the voltage over electrodes' filaments during dimming operation. The lamp model employed in this paper is based on equivalent resistances, which represent the electrodes' filaments and the gas column of a F32T8 lamp. Experimental results are presented in this paper, indicating the validity of the proposed analysis and confirming its potential to serve as an effective tool for the design of dimming electronic ballasts. © 2005 IEEE.

An AC voltage regulator with high-power-factor, and control using a FPGA device

This paper presents the analysis, design, simulation, and experimental results for a high frequency high Power-Factor (PF) AC (Alternate Current) voltage regulator, using a Sepic converter as power stage. The control technique employed to impose a sinusoidal input current waveform, with low Total Harmonic Distortion (THD), is the sinusoidal variable hysteresis control. The control technique was implemented in a FPGA (Field Programmable Gate Array) device, using a Hardware Description Language (VHDL). Through the use of the proposed control technique, the AC voltage regulator performs active power-factor correction, and low THD in the input current, for linear and non-linear loads, satisfying the requirements of the EEC61000-3-2 standards. Experimental results from an example prototype, designed for 300W of nominal output power, 50kHz (switching frequency), and 127Vrms of nominal input and output voltages, are presented in order to validate the proposed AC regulator. © 2005 IEEE.

Phylogenetic analysis of flatfish (order pleuronectiformes) based on mitochondrial 16s rDNA sequences

The phylogenetic relationships of the order Pleuronectiformes are controversial and at some crucial points remain unresolved. To date most phylogenetic studies on this order have been based on morpho-anatomical criteria, whereas only a few sequence comparisons based studies have been reported. In the present study, the phylogenetic relationships of 30 flatfish species pertaining to seven different families were examined by sequence analysis of the first half of the 16S mitochondrial DNA gene. The results obtained did not support percoids as the sister group of pleuronectiforms. The monophyletic origin of most families analyzed, Soleidae, Scophthalmidae, Achiridae, Pleuronectidae and Bothidae, was strongly supported, except for Paralichthyidae which was clearly subdivided into two groups, one of them associated with high confidence to Pleuronectidae. The analysis of the 16S rRNA gene also suggested the monophyly of Pleuronectiforms as the most probable hypothesis and consistently supported some major interfamily groupings.