Histologia branquial de Rhamdia quelen saudáveis e infectados com Aeromonas hydrophila expostos a diferentes isoformas de limoneno

Abstract

The growth of Brazilian fish culture and the consequent increase of diseases caused by bacteria, such as Aeromonas hydrophila, has caused the abuse of synthetic drugs and chemicals. In addition to the indiscriminate use of antimicrobials to trigger bacterial resistance, their use favors the deposition of residues in animal tissues, causes immunosuppression and contaminates the aquatic environment. Based on this, aquaculture has shown a greater interest in the use of plant essential oils as a source of prophylactic and therapeutic medicine. Most essential oils contain compounds that have antimicrobial, antiparasitic, antifungal and anti-inflammatory properties. Limonene is a monoterpene present in essential oils of citrus plants, available in nature in the enantiomeric forms R-(+)-limonene and S-(-)-limonene. Given the importance of pathogen control in aquaculture, the objective of this study was to evaluate the effects of the R-(+)-limonene and S-(-)-limonene isoforms on the histological parameters of the gills of healthy and Aeromonas hydrophila infected Rhamdia quelen. In the first experiment, healthy fish were divided into seven groups: control, 10 mg/L gentamicin, 90 μL/L ethanol, 10 μL/L R-(+)-limonene, 20 μL/L R-(+)-limonene, 10 μL/L S-(-)-limonene, 20 μL/L S-(-)-limonene and exposed once to treatments. In the second experiment the fish were divided into ten groups: control, 10 mg/L gentamicin, 90 μL/L ethanol, 10 μL/L R-(+)-limonene, 20 μL/L R-(+)-limonene, exposed once to treatments and inoculated or not with A. hydrophila. Exposure to S-(-)-limonene caused the death of some fish and also induced signs of gill tissue inflammation, such as lamellar edema, lamellar fusion, infiltration of inflammatory cells in connective tissue, proliferation of mucous cells and ionocytes. On the other hand, in the gills exposed to the R-(+)-limonene isoform no changes were observed in these parameters. The gills of fish infected with A. hydrophila also showed signs of inflammation, in addition to increased thickness of filamentous epithelium, lamellar and connective tissue. The lamellae were reduced in length and interlamellar space. Aneurysm formation, increased number of mucous cells and ionocytes and in the size of mucous cells were observed. However, in fish infected and treated with R-(+)-limonene the changes were less intense. In conclusion, S-(-)-limonene was shown to be irritating to silver catfish, causing deaths and inducing inflammation and histopathological changes. On the other hand, R-(+)-limonene protected against gill inflammation, being the most suitable for fish infected with A. hydrophila, preferably at 10 μL/L R-(+)-limonene concentration.