EFFECT OF THE HERBICIDE 2,4-DICHLOROPHENOXYACETICACID (2,4-D) ON GILLS OF AN INTESTINAL BREATHER PEPPERED LOACH LEPIDOCEPHALICHTHYS GUNTEA

摘要

Effect of sub-lethal exposure (30 mg/litre) of the herbicide,2,4-dichlorophenoxy acetic acid has been studied on the gills of an air breathing fish, Lepidocephalichthys guntea. Two types of toxic effect-lesions and reactions are observed in gill in present investigation.Lesions are characterized by degenerative changes in epithelial cells at different regions of the gill and reaction includes epithelial lifting, fusion of gill lamellae, hypertrophy. Degeneration in epithelial cells in gill arch, gill filament and gill lamellae of Lepidocephalichthys guntea at different durations of 2,4-D treatment is characterized by nuclear pyknosis,breaking of cell membrane,cytoplasmic disintegration and exfoliation of epithelial cells. Up liftment of epithelial cells in gill lamellae from basement membrane of the pillar cells leaving sub-epithelial space between pillar cell system and epithelial lining at different duration of the herbicide treatment has been correlated to diminish effective osmoregulatory surface in addition to the possibilities of normal gas exchange since the water flow through the above region is reduced. Fusion of gill lamellae at different exposures of the herbicide has been correlated to reduce pollutant intake. The gill filament epithelial cells in interlamellar space show hyperplasia which contribute to the reduction of inter lamellar spaces minimizing passage between two adjacent lamellae for entering water containing toxicants. Swelling of lamellae has been correlated to increase diffusion distance between water and blood and thus being responsible for respiratory impairment and delay the arrival of the herbicide dissolved in water to blood channels of pillar cell system. Increase in density and dimension of mucous cells are related to enhance mucous secretion which is an inbuilt defence mechanism of the fish against disturbed aquatic environment. Appearance of telangiectatic gill lamellae is due to dilation of capillaries and it adversely affects oxygen uptake efficiency of gills. Fatal haemorrhage due to rupture of telangiectasia also occurs. At late exposures normal microanatomy of lamellae with their blood channels,pillar cells and epithelial units get distorted and the blood is haemolysed. The haemolysis of lamellar blood causes hypoxemia and fishes leave their hiding places to float on water surface in search of oxygen.