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Collections over four years in the habitat of submerged litter show that shrimps are abundant the year round. Mean densities vary from 5-45 animals/m of litter habitat. Finegrained density distribution within litter sites is highly clumped, but coarse-grained distribution in any given month between litter sites along the river is grosso-modo random.Density and species distribution are a function of the annual cycles of inundations. Of the five species (of a total of seven in the area) that were found to be breeding in the litter habitat it could be established that reproduction is restricted to the period of rising and highest water levels. Reproduction is low in all species, namely below 20 eggs per egg batch with essentially a single generation per year.Breeding ecology in relation to the litter habitat is briefly discussed.

We analyzed one Bunocephalus coracoideus population from the Negro River basin using cytogenetic techniques. The results showed a diploid number of 42 chromosomes in both sexes, with the karyotypic formula 4m + 14sm + 24a and fundamental number (FN) = 60 for females and the formula 5m + 14sm + 23a and FN = 61 for males, constituting an XXXX/XYXY multiple sex chromosome system. The constitutive heterochromatin is distributed in the pericentromeric regions of most of the chromosomes, except for the sex chromosomes, of which the X, X, and Y chromosomes were euchromatic and the Y chromosome was partially heterochromatic. 18S rDNA mapping confirmed the presence of nucleolar organizer regions on the short arms of the fifth chromosomal pair for both sexes. The 5S rDNA is present in the terminal regions of the short arms on the 2nd, 10th, and 12th pairs and on the X chromosome of both sexes; however, we observed variations in the presence of these ribosomal cistrons on the Y chromosome, on which the cistrons are pericentromeric, and on the Y chromosome, on which these cistrons are present in the terminal portions of the short and long arms. Telomeric sequences are located in the terminal regions of all of the chromosomes, particularly conspicuous blocks on the 10th and 12th pairs and internal telomeric sequences in the centromeric regions of the 1st, 6th, and 9th pairs for both sexes. This work describes an new sex chromosomes system for the Siluriformes and increases our genetic knowledge of the Aspredinidae family.

Farlowella is one of the most diverse genera of the Loricariinae, restricted to South America rivers. The taxonomic and phylogenetic relationships among its species are contentious and, while genetic studies would contribute to the understanding of their relationships, the only available datum refer to the karyotype description of only one species. In the present study two Amazonian species, Farlowella cf. amazonum and F. schreitmuelleri, were analyzed using conventional and molecular cytogenetic procedures. Both species had diploid chromosome number 58, but different fundamental numbers (NF) 116 and 112, respectively, indicative of chromosomal rearrangements. C-banding is almost poor, especially in F. cf. amazonum, and occurs predominantly in the centromeric and in some telomeric regions, although genome of F. schreitmuelleri possessed a much larger heterochromatin amount then those of F. cf. amazonum. The chromosomes bearing the NOR sites were likely the same for both species, corresponding to the 1st metacentric pair in F. cf. amazonum and to the 28th acrocentric in F. schreitmuelleri. The location of the 5S rDNA was species-specific marker. This study expanded the available cytogenetic data for Farlowella species and pointed the remarkable karyotype diversity among species/populations, indicating a possible species complex within genus.

Bunocephalus is the most species-rich Aspredinidae genus, corresponding to a monophyletic clade with 13 valid species. However, many species have their classification put in question. Here, we analyzed individuals from four Amazonian populations of Bunocephalus coracoideus by cytogenetic and molecular procedures. The geographic distribution, genetic distances and karyotype data indicate that each population represents an Evolutionary Significant Unit (ESU). Cytogenetic markers showed distinct 2n and karyotype formulas, as well as different numbers and locations of the rDNA sites among ESUs. One of such populations (ESU-D) highlighted an extensive polymorphic condition, with several cytotypes probably due to chromosomal rearrangements and meiotic non-disjunctions. This resulted in several aneuploid karyotypes, which was also supported by the mapping of telomeric sequences. Phylograms based on Maximum Likelihood (ML) and Neighbor Joining (NJ) analyses grouped each ESU on particular highly supported clades, with the estimation of evolutionary divergence indicating values being higher than 3.8–12.3% among them. Our study reveals a huge degree of chromosomal and genetic diversity in B. coracoideus and highly points to the existence of four ESUs in allopatric and sympatric speciation processes. In fact, the high divergences found among the ESUs allowed us to delimitate lineages with taxonomic uncertainties in this nominal species.

The genus Colomesus is the sole representative of the family Tetraodontidae in the Amazon region. Here, Colomesus asellus was analyzed using conventional and molecular cytogenetic protocols. Its diploid chromosome number is 2n = 46 with 12 meta-, 10 submeta-, 16 subtelo-, and 8 acrocentric chromosomes and a fundamental number of FN = 84. An XX/XY sex chromosome system was identified. Mapping of 18S rDNA correlated with the nucleolus organizer regions (Ag-NORs) in the short arms of the 2 X chromosomes in females and in the Y chromosome in males. C-banding revealed heterochromatin in the centromeric regions of all chromosomes, except for pair 3. Prominent sex chromosome-specific heterochromatin amplification was observed, covering the short arms of the Y chromosome almost entirely. FISH with telomeric and tropomyosin (tpm1) sequences, respectively, revealed terminal signals in all chromosomes. The analysis of extended DNA fibers confirmed the colocalization and the interspersed pattern of the telomeric and tpm1 sequences. Thus, this study highlights the remarkable evolutionary dynamism presented by the Amazonian puffer fish regarding the differentiation of a heteromorphic XY sex chromosome system and a particular sex-specific amplification of rDNA sites. This is the first record of such an association in the Tetraodontidae family.

ABSTRACT. Pimelodus (Pimelodidae) is a genus comprising a group of South American species with complex taxonomic relationships. Cytogenetics, polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP), and sequencing data of mitochondrial genes were analyzed to characterize 4 Pimelodus species: P. fur, P. heraldoi, P. maculatus, and Pimelodus sp. All populations presented 2n = 56 chromosomes and distinct karyotypic formulae. The heterochromatin distribution pattern and the number and location of 5S and 18S rDNA sites are discussed. The application of PCR-RFLP markers and sequencing of mitochondrial DNA genes provided species-specific haplotypes, which allowed us to differentiate the species studied. The mitochondrial gene sequences presented nucleotide mutations in the restriction sites and throughout the sequences, and they were mostly related to synonymous substitutions in the coded proteins; however, they did not affect the protein and its function. Comparing the data obtained using these 3 methodologies, the existence of a species complex in P. maculatus along the basins studied might be inferred, showing that cytogenetics is an important tool in studies focusing on the conservation or management of both natural and captive populations of these fishes.

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