A Perspective of Molecular Cytogenomics, Toxicology, and Epigenetics for the Increase of Heterochromatic Regions and Retrotransposable Elements in Tambaqui (Colossoma macropomum) Exposed to the Parasiticide Trichlorfon

SIMPLE SUMMARY: The aim of the present study was to evaluate the Trichlorfon effects on the retrotransposable elements in tambaqui (Colossoma macropomum) genome, which is a highly popular and well-known fish in the Amazon with a large reproduction number mediated by pisciculture. Thereby, tambaqui specimens were submitted to two different Trichlorfon concentrations (30% and 50% of LC(50–96 h)) under experimental conditions. The retrotransposons were analyzed using the FISH technique and the heterochromatin standard with the C-band technique. The retrotransposons studied presented a dispersed distribution profile in the tambaqui karyotype with Rex3 being more prominent than the others, showing the greatest increase in markings. Furthermore, the heterochromatin profile showed that these retrotransposons can be found in the heterochromatic portions of the chromosomes. Thus, it was observed that Trichlorfon has an activation mechanism for these retroelements, especially Rex3. ABSTRACT: Rex retroelements are the best-known transposable elements class and are broadly distributed through fish and also individual genomes, playing an important role in their evolutionary dynamics. Several agents can stress these elements; among them, there are some parasitic compounds such as the organochlorophosphate Trichlorfon. Consequently, knowing that the organochlorophosphate Trichlorfon is indiscriminately used as an antiparasitic in aquaculture, the current study aimed to analyze the effects of this compound on the activation of the Transposable Elements (TEs) Rex1, Rex3, and Rex6 and the structure of heterochromatin in the mitotic chromosomes of the tambaqui (Colossoma macropomum). For this, two concentrations of the pesticide were used: 30% (0.261 mg/L) and 50% (0.435 mg/L) of the recommended LC(50–96 h) concentration (0.87 mg/L) for this fish species. The results revealed a dispersed distribution for Rex1 and Rex6 retroelements. Rex3 showed an increase in both marking intensity and distribution, as well as enhanced chromosomal heterochromatinization. This probably happened by the mediation of epigenetic adaptive mechanisms, causing the retroelement mobilization to be repressed. However, this behavior was most evident when Trichlorfon concentrations and exposure times were the greatest, reflecting the genetic flexibility necessary for this species to successfully adapt to environmental changes.