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Loricariidae (Siluriformes) comprises ∼1026 species of neotropical fish, being considered the most diverse among the Siluriformes. Studies on repetitive DNA sequences have provided important data on the evolution of the genomes of members of this family, especially of the Hypostominae subfamily. In this study, the chromosomal mapping of the histone multigene family and U2 snRNA was performed in two species belonging to the Hypancistrus genus, Hypancistrus sp. "pão" (2n = 52, 22m + 18sm +12st) and Hypancistrus zebra (2n = 52, 16m + 20sm +16st). The presence of dispersed signals of histones H2A, H2B, H3, and H4 in the karyotype of both species, with each sequence displaying a varied level of accumulation and dispersion of these sequences between them was observed; in addition, U2 snDNA probe only showed positive results in H. zebra , which present this multigene in the terminal region of three chromosomal pairs. The obtained results resemble data already analyzed in the literature, in which the action of transposable elements interfere in the organization of these multigene families, in addition to other evolutionary processes that shape the evolution of the genome, such as circular or ectopic recombination. This study also shows that the dispersion of the multigene histone family is quite complex, and from this, these data serve as a point of discussion for the evolutionary processes that occur in the Hypancistrus karyotype.

Ecotoxicological assessment is an useful tool to evaluate toxicity of pollutants on aquatic organisms. In the present study, we evaluated the lethal effect, micronucleus frequency and histological changes in gills of fish species Danio rerio exposed to water from two sources of a Conservation Unit. We performed acute tests, Micronucleus Test in blood cells and histological analysis of gills. As results, the springs had no lethal toxic effects on the species. Nuclear alterations were present in erythrocytes in organisms exposed to water from the two sampled sites. As well, we found moderate to severe gill abnormalities generating the impairment of respiratory vital functions of these organisms. This study indicates that the water of the springs does not present lethal toxic effect but damage in gills for species from short exposure time.