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.

Producers of fish have been looking for viable alternatives for the management of Colossoma macropomum (tambaqui) in confinement systems in order to avoid the harm and subsequent losses caused by parasitic diseases. One alternative used by farmers is pesticides, such as trichlorfon, which has a genotoxic effect. Thus, this study aimed to evaluate the changes in gene expression due to the side effects of trichlorfon in tambaqui. Two treatments were used based on LC₅₀-96h of 0.870 mg/L using 30% and 50% trichlorfon with exposure periods of 48, 72 and 96 h. For differential expression of the genes in the liver, real-time PCR was performed for the AChE, GST, CYP2J6, CYP2C8, 18S and GAPDH genes. After 96 h of exposure to trichlorfon, an alteration in the gene expression profile of the antioxidant defense system (GST) of the tambaqui was observed. It was also observed that this organophosphate did not affect the expression of genes related to the isoenzymes that are responsible for the biotransformation of xenobiotics in phase I (2J6 and 2C8) and cholinesterase AChE. It was concluded that the reduction in gene expression of GST suggests a decrease in metabolization capacity in phase II.

Trichlorfon is an antiparasitic agent widely used to control pests and parasites in farmed fish. Tambaqui (C. macropomum) is the most commercially important characid species farmed in the Amazon region. Trichlorfon exposure is known to cause physiological damage in fish due to its organophosphate nature. In this study, we used RNA-Seq to investigate the hepatic response of tambaqui following exposure to 0.435 mg/L of trichlorfon. The analysis revealed activation of several metabolic pathways, particularly those related to tumor processes, immune responses, and apoptosis. Additionally, we identified upregulation of solute carrier (SLC) genes, which may facilitate trichlorfon entry into hepatocytes. These findings enhance our understanding of fish responses to antiparasitic agents and support further research into the molecular impacts of organophosphate compounds in aquaculture species.

Austrodiplostomum Szidat & Nani, 1951 is a genus of parasitic digenetic trematodes widely distributed in the Neotropical region. Infects a wide variety of species, families and requests for freshwater fish. We identify samples of Austrodiplostomum sp, based on metacercariae isolates from eyes of tambaqui (Colossoma macropomum), a fish of high commercial importance in Brazil, and widely consumed by the population of the northern region. The sequences obtained clustered with A. compactum. This is the first report of the occurrence of diplostomids in farmed tambaqui in Amazonia.