Effects of the organophosphorous methyl parathion on the branchial epithelium of a freshwater fish Metynnis roosevelti

Abstract

Gills are vital structures for fish, since they are the main site for gaseous exchange as well as partially responsible for osmorregulation, acid-basic balance, excretion of nitrogenous compounds and taste. Chemicals in the water may alter the morphology of branchial cells of fish that are, therefore, a useful model for environmental impact and ecotoxicology studies. In order to investigate the effects of an organophosphorous compound, methyl parathion, on the gills of the fish, samples of Metynnis roosevelti were exposed to lethal (7ppm) and sublethal (1ppm) doses of Mentox 600 CE. Through light and scanning electron microscopy, shrinking of the branchial epithelium, followed by detachment and hyperplasia were observed. Externally, the branchial filaments presented the gradual disappearance of microridges. Even in sublethal doses, the organophosphorous reduced the health and fitness of these fish, as consequence of secondary effects derived from changes in the branchial epithelium, impairing oxygenation and ionic balance of the organism.<br>As brânquias são estruturas vitais para peixes, pois são o principal local de trocas gasosas, assim como parcialmente responsáveis pela osmorregulação, pelo equilíbrio ácido-básico, pela excreção de compostos nitrogenados e pela gustação. Compostos químicos na água podem alterar a morfologia das células branquiais de peixes, que se constituem, dessa forma, em um útil modelo para estudos de impacto ambiental. Visando investigar os efeitos de um composto organofosforado, o metil paration, em brânquias de peixes, exemplares de Metynnis roosevelti foram expostos a doses letais (7ppm) e subletais (1ppm) de Mentox 600 CE. Observações em microscopia óptica e eletrônica de varredura evidenciaram enrugamento do epitélio branquial, seguido por descolamento e hiperplasia. Externamente, os filamentos branquiais apresentaram desaparecimento gradual das microssaliências. Os resultados mostram que, mesmo em doses subletais, o organofosforado poderá levar o animal a sofrer conseqüências secundárias decorrentes das alterações da superfície de trocas gasosas e iônicas

Gills of juvenile fish piaractus mesopotamicus as histological biomarkers for experimental sub-lethal contamination with the Organophosphorus Azodrin®400

“…Morphological biomarkers are useful tools for the determination of the effect of pollutants on fish. Gills are considered the most vulnerable organ to the changes in the aquatic environment (Dutta et al, 1996), because they are in direct contact with the surrounding water that may contain OPs and, consequently, they are the first entrance door for these and other pollutants (Machado and Fanta, 2003). Detailed description of each pathology, mainly through electron microscopy, and the quantification of the pathologies observed in the gills of P. mesopotamicus in the present study allowed an evaluation of the degree of damage and the potential consequences for the fish.…”

“…This implies in an increase in the diffusion distance of oxygen, as seen in P. mesopotamicus that condition can affect the respiration of the fish, even resulting in their death (Dutta et al, 1993). Several studies have described acute exposure of fishes to other OPs such as malathion (Capinpin, 1994;Richmonds and Dutta, 1989), diazinon (Dutta et al, 1993) and methyl parathion Machado and Fanta, 2003). Considering that the extent of the epithelial detachments may be related to the seriousness of the consequences for the fish, they were described and classified in this study from minimal to severe and intense.…”

“…This was also observed by Richmonds and Dutta (1989) in Lepomis macrochirus after 48 h of exposure to the OP Malathion, and by Fanta et al (2003) in Corydoras paleatus. This possibly occurs because freshwater fishes are hyperosmotic in relation to the environment, what favours the influx of water through the lesioned epithelium, increasing the hydropsy, and consequently the epithelial detachment (Machado and Fanta, 2003). Such condition increases the distance that the toxic substances have to travel to reach the blood stream, and therefore epithelial detachment could be considered as a defence mechanism against the entrance of excessive water pollutants after 48 hours of exposure (Dutta et al, 1993).…”

“…However, at sub lethal levels, OP pesticides can change significantly some physiological and biochemical processes, and even the morphology of several tissues when they enter the fish organism (Silva et al, 1993;Sancho et al, 1992). Fish gills are sensitive to many classes of chemical pollutants dissolved in water because they are in direct contact with the aquatic environment, and any damage in their structure can interfere with respiration and the ionic homeostasis (Machado and Fanta, 2003;Van den Heuvel et al, 2000). Histological alterations constitute excellent biomarkers of exposure to toxicants because they represent the result of biochemical and physiological changes (Hinton et al, 1989).…”

“…Histological alterations constitute excellent biomarkers of exposure to toxicants because they represent the result of biochemical and physiological changes (Hinton et al, 1989). The most common injuries in gills are epithelial detachment (Machado and Fanta, 2003;Mallatt, 1985;Richmonds and Dutta, 1989;Schwaiger et al, 2004), hyperplasia (Annune and Ajike, 1999;Dutta et al, 1993;Fanta et al, 2003;Oliveira Ribeiro et al, 1996), fusion of secondary lamellae (Capinpin, 1994;Karan et al, 1998;Thophon et al, 2003) and aneurysm (Stentiford et al, 2003;Thophon et al, 2003;Van den Heuvel et al, 2000). Piaractus mesopotamicus is a freshwater native fish from tropical and subtropical rivers of the Paraná-Paraguay Basin and from flooded areas of the Pantanal region (State of Mato Grosso, Brazil) (Severi et al, 1997;Lima et al, 1998).…”