Scinax Wagler, 1830 is a species-rich genus of amphibians with relatively few detailed chromosomal reports. In this work, cytogenetic analyses of Scinax auratus (Wied-Neuwied, 1821) and Scinax eurydice (Bokermann, 1968) were carried out based on conventional (Giemsa staining, Ag-NOR and C-banding) and cytomolecular (base-specific fluorochrome staining and fluorescence in situ hybridization – FISH of ribosomal probes) techniques. Both species shared the same karyotype, location of active nucleolar organizer regions on pair 11 and GC-rich heterochromatin, as reported for most species in Scinax ruber clade. Interpopulation chromosomal variation was observed in Scinax eurydice, indicating the occurrence of cryptic species. The mapping of 18S ribosomal genes by FISH is reported for the first time in both species.

The weakness of physical barriers in the marine environment and the dispersal potential of fish populations have been invoked as explanations of the apparent karyotype stasis of marine Percomorpha, but several taxa remain poorly studied cytogenetically. To increase the chromosomal data in this fish group, we analyzed cytogenetically three widespread Atlantic species from distinct families: Chaetodipterus faber Broussonet, 1782 (Ephippidae), Lutjanus synagris Linnaeus, 1758 (Lutjanidae) and Rypticus randalli Courtenay, 1967 (Serranidae). The three species shared a karyotype composed of 2n=48 acrocentric chromosomes, single nucleolus organizer regions (NORs) and reduced amounts of centromeric heterochromatin. A single NOR-bearing pair was identified in all species by physical mapping of 18S rDNA while non-syntenic 5S rRNA genes were located at centromeric region of a single pair. The similar karyotypic macrostructure observed in unrelated groups of Percomorpharia reinforces the conservative karyoevolution of marine teleosteans. Nonetheless, the species could be differentiated based on the pair bearing ribosomal cistrons, revealing the importance of microstructural analyses in species with symmetric and stable karyotypes.

Mullets are very common fishes included in the family Mugilidae, (Mugiliformes), which are characterized by both a remarkably uniform external morphology and internal anatomy. Recently, within this family, different species complexes were molecularly identified within Mugil, a genus which is characterized by lineages that sometimes show very different karyotypes. Here we report the results of cytogenetic and molecular analyses conducted on Mugil hospes, commonly known as the hospe mullet, from Ecuador. The study aims to verify whether the original described species from the Pacific Ocean corresponds to that identified in the Atlantic Ocean, and to identify species-specific chromosome markers that can add new comparative data about Mugilidae karyotype evolution. The karyotype of M. hospes from Ecuador is composed of 48 acrocentric chromosomes and shows two active nucleolar organizer regions (NORs). In situ hybridization, using different types of repetitive sequences (rDNAs, U1 snDNA, telomeric repeats) as probes, identified species-specific chromosome markers that have been compared with those of other species of the genus Mugil. Cytochrome c oxidase subunit I (COI) sequence analysis shows only 92–93% similarity with sequences previously deposited under this species name in GenBank, all of which were from the Atlantic Ocean. Phylogenetic reconstructions indicate the presence of three well-supported hospe mullet lineages whose molecular divergence is compatible with the presence of distinct species. Indeed, the first lineage includes samples from Ecuador, whereas the other two lineages include the Atlantic samples and correspond to M. brevirostris from Brazil and Mugil sp. R from Belize/Venezuela. Results here provided reiterate the pivotal importance of an integrative molecular and cytogenetic approach in the reconstruction of the relationships within Mugilidae.

The guitarfishes Pseudobatos horkelii and Pseudobatos percellens meet the criteria for threatened status as Critically Endangered (CR) and Endangered (EN), respectively. Both species occur in the Southern Atlantic Ocean. Considering the lack of data on the genetic structure of these species, the present study evaluated the genetic variability and population structure of the P. horkelii and P. percellens in the southern region of Brazil and the northern coast of Argentina, based on sequences of mitochondrial DNA, Control Region (D-loop). Samples of P. horkelii (n = 135) were analyzed in six localities situated in Northern Argentina, along the Brazilian states’ coast. The mean of nucleotide diversity was 0.0053, the ΦST was 0.4277 and demographic analysis of P. horkelii suggests the existence of stability of the populations, with D = 0.9929, FS = 2.0155, SSD = 0.0817, R = 0.2153. In P. percellens (n = 101) were analyzed from six Brazilian localities along the coast of Santa Catarina, Paraná, and São Paulo. The mean nucleotide diversity was 0.0014 and ΦST value of 0.2921, the demographic analysis indicates a high migration rate of P. percellens among the localities evaluated, with D = 0.5222, FS = 0.3528, SSD = 0.01785, R = 0.3890.

The chromosomes of two freshwater stingrays, Potamotrygon motoro and Potamotrygon sp., from the Amazon River basin in Brazil were investigated using integrated molecular (cytochrome c oxidase subunit 1) and cytogenetic analyses. Potamotrygon motoro presented intraspecific variation in the diploid number, with 2n=66 in the females and 2n=65 in the males, while Potamotrygon sp. had a karyotype with 66 chromosomes, in both sexes. The C-banding revealed the presence of heterochromatic blocks accumulated in the centromeric region of all the chromosomes in both species. The FISH assays with 18S DNA probes highlighted the terminal region of three or four chromosome pairs in P. motoro and seven chromosomes in Potamotrygon sp. The rDNA 5S sequences were found in only one chromosomal pair in both species. The interspecific genetic distance based on the COI sequences, between P. motoro and Potamotrygon sp. from Amazon River was 10.8%, while that between the Amazonian P. motoro and Potamotrygon amandae from the Paraná River was 2.2%, and the genetic distance between Potamotrygon sp. and P. amandae was 11.8%. In addition to the new insights on the cytogenetics of the study species, the results of the present study confirmed the existence of heteromorphic sex-linked chromosomes in P. motoro.

In this study, we present descriptions, illustrations, comments, and bathymetric and geographic distributions of the brittle star species related to the estuary region of Camamu Bay, located in the State of Bahia, Brazil. The brittle star fauna lives on biological substrates, sand bottoms, mud and rubble in the Camamu Bay and comprises 12 species divided into five families. Almost all of them are common in the tropical and subtropical fauna of the regions of shallow water. Ophiophragmus filograneus is reported for the first time in Bahia, and nine other species are recorded for the first time in Camamu Bay: Amphipholis januarii, Amphipholis squamata, Ophiophragmus filograneus, Ophiostigma isocanthum, Ophioderma cinerea, Ophioderma januarii, Ophiactis lymani, Ophiactis savignyi and Ophiocoma echinata. The results suggest that the ophiuroid assemblages are strongly affected by marine currents as well as by different kinds of bottom substrate.

Cell culture is an excellent alternative for the maintenance of cell lines and to obtain quality chromosome preparations of fishes. However, this methodology is still little employed, mainly because of the difficulty of standardization of cell cultures. In this study, we describe a methodology for the rapid acquisition of cell lineages and mitotic chromosomes for cytogenetic studies of fish species from muscle tissue cells. Our methodology is based on the use of a gelatin film, which provides better adhesion of a large number of cells and appropriate conditions for multiplication. The cells of Astyanax altiparanae, used as an experimental model, with fibroblast-like morphology, showed rapid cellular proliferation, resulting in a great number of cells. Chromosomal preparations of cultured cells showed the diploid number of the species, 2n = 50 chromosomes, in 80% of the cells examined, with chromosomes intact and distended. Cell populations were cryopreserved and after being recovered, these cells maintained their proliferative capacity. The development of this methodology represents an innovation for the fish cytogenetics area and it may bring a significant contribution to the conservation and study of several groups due to the difficulty of obtaining good-quality chromosome preparations.

The freshwater fish species Dormitator latifrons, commonly named the Pacific fat sleeper, is an important food resource in CentralSouth America, yet almost no genetic information on it is available. A cytogenetic analysis of this species was undertaken by standard and molecular techniques (chromosomal mapping of 18S rDNA, 5S rDNA, and telomeric repeats), aiming to describe the karyotype features, verify the presence of sex chromosomes described in congeneric species, and make inferences on chromosome evolution in the genus. The karyotype (2n = 46) is mainly composed of metacentric and submetacentic chromosomes, with nucleolar organizer regions (NORs) localized on the short arms of submetacentric pair 10. The presence of XX/XY sex chromosomes was observed, with the X chromosome carrying the 5S rDNA sequences. These heterochromosomes likely appeared before 1 million years ago, since they are shared with another derived Dormitator species (Dormitator maculatus) distributed in the Western Atlantic. Telomeric repeats hybridize to the terminal portions of almost all chromosomes; additional interstitial sites are present in the centromeric region, suggesting pericentromeric inversions as the main rearrangement mechanisms that has driven karyotypic evolution in the genus. The data provided here contribute to improving the cytogenetics knowledge of D. latifrons, offering basic information that could be useful in aquaculture farming of this neotropical fish.