Fresh water paddy field crab Paratelphusa hydrodromus were exposed to sub-lethal concentration of arsenic (22.8 ppm) (1/5th of LC50 concentration) for 72 hours along with 48 hours recovery of 72 hrs exposed animals to toxicant free water. The gill morphological alterations were examined by light microscope using semi-quantitative histopathological evaluation. The morphometric measurements were collected from the five different points and examined the width of basal septum, lamellae, apical protuberance in both control and treated organisms exposed to arsenic. Light microscopic examination of the toxicant treated gill revealed serious gross morphological alterations against control animals and were time dependent. The gill after 2 hrs of exposure showed enlargement of branchial septum, lamellae and apical protuberance. The gills fixed after 24 hrs of arsenic exposure showed alteration in the haemolymph flow pattern, haemocyte infiltration and enlargement of branchial septum. In 24 and 48 hrs exposure, pilaster bridging in the lamellae were almost normal and brachial podocyte distribution was dense in the anterior region and gradually decrease towards the posterior edges and leaving large haemal space. Extensive infiltration of haemocytes and focal necrosis was observed in the few lamellae along with clumping of haemocytes and epithelial hyperplasia. During 48 hrs recovery treated animals showed enlargement of lamellae with subepithelial edema at the apical protuberances region. The animals transferred to toxicant free water showed quick changes like enlargement of lamellae and branchial septum. Disappearance of pilaster cells and lifting of cuticle from epithelial layer were also noticed during the recovery phase.
