Respostas de cortisol e danos histopatológicos em tilápias-do-nilo (Oreochromis niloticus) expostas ao herbicida roundup ready

Abstract

The study investigated histopathological damage and the endocrine disruption caused by the herbicide roundup ready [combination of isopropylamine salt of glyphosate, acid equivalent N-(phosphonomethyl) and glycine] in juvenile Nile tilapia (Oreochromis niloticus). First, we determined the LC50-48h for the herbicide calculated in 2.94 mg / L (confidence interval 2.77 to 3.13 mg / L). Second, chronic exposure took place for 14 days, at sublethal concentrations of the herbicide (1%, 2%, 10% and 20% of LC50-48 hr). Third, the fish were acutely exposed to sublethal concentrations of the herbicide (1%, 2%, 10% and 20% of LC50-48h) for a period of 48 h combined with a stressor stimulus. At the end of each acute and chronic exposure, surviving fish were anesthetized and proceeded with the removal of organs for histopathological analysis. In the chronic exposure, the death of all fishes at all concentrations occurred from the eleventh day exposure. At the end of the test, mortality rates of 6.25%, 31.24%, 17.64%, and 20, were observed in the groups exposed to the concentrations of 1%, 2%, 10%, and 20% of LC50-48h respectively. In the histopathological analysis, the main lesions caused by the toxic compound both in acute and chronic exposure, were detected in the gills (hemorrhagie, congestion and inflammatory infiltrate) in the liver (degeneration, hepatocyte necrosis and cholestasis) and kidneys (degeneration and necrosis), attempting to renal lesions, followed by gills and liver lesions, what suggests intoxication. The stress responses of all treatments were compared with those who had not been exposed to treatment (control group) or were exposed only to the estressor (stressed group). Fingerlings were exposed to the highest sublethal concentrations of the herbicide, increased cortisol levels with values similar to those found in the group submitted to stressor. Hower, in contrast, the exposed juveniles to all concentrations of roundup ready in combination with an acute stressor, showed significantly lower cortisol levels than those found in the control group, suggesting that the herbicide attenuates the cortisol response. In this context we may conclude that herbicide rondup ready is moderately toxic to Oreochromis niloticus at sublethal concentrations, courses lethality and irreversible damage to the body, also leading to an enchance in cortisol concentrations at 10% and 20% LC50-48h. But when combined with a stressor, all concentrations provoke an inibition of the elevation of cortisol. Our results indicate that extreme ccantion must be adopt, in the use of these compounds, in lend to prevent deleterious effects in fish and preseve its homeostasis.