~ 93 ~ International Journal of Fisheries and Aquatic Studies 2019; 7(3): 93-98 E-ISSN: 2347-5129 P-ISSN: 2394-0506 (ICV-Poland) Impact Value: 5.62 (GIF) Impact Factor: 0.549 IJFAS 2019; 7(3): 93-98 © 2019 IJFAS www.fisheriesjournal.com Received: 07-03-2019 Accepted: 09-04-2019 Smriti Batoye Department of Zoology, Maharaja Agrasen University, Baddi, Himachal Pradesh, India Rajinder Jindal Aquatic Biology Lab, Department of Zoology, Panjab University, Chandigarh, India Sakshi Verma Zoology Department, HMV, Jalandhar, Punjab, India Correspondence Smriti Batoye Department of Zoology, Maharaja Agrasen University, Baddi, Himachal Pradesh, India Scanning electron microscopic investigation on the scales of grass carp, Ctenopharyngodon idellus (Cuvier and Valenciennes) exposed to lead nitrate Smriti Batoye, Rajinder Jindal and Sakshi Verma Abstract The aquatic ecosystem is the most affected ecosystem due to contamination of heavy metals. The present investigation was undertaken to assess the toxicity of lead nitrate on the scales of Ctenopharyngodon idellus. Acute toxicity test was conducted to evaluate 96 h LC50 of lead nitrate to C. idellus and was found to be 33.27 mg/L. For Chronic bioassay studies, two sublethal concentrations (i.e. 6.65 mg/L and 11.09 mg/L) of 96 h LC50 of lead nitrate were selected for 45 days. Fish exposed to sublethal concentrations of the toxicant showed hyper excitability, erratic swimming, jerky movements and tendency to escape from aquaria, increase in the rate of air gulps, fin and opercular movements. Loosening of scales, excess secretion of mucus and depigmentation were the morphological alterations. The ultrastructural changes on the scales of C. idellus were observed using scanning electron microscope (SEM). The scales showed various degrees of deformity to the circuli and tubercles on exposure to lead nitrate. Keywords: Ctenopharyngodon idellus, lead nitrate, scanning electron microscope, scales, grass carp, heavy metals 1. Introduction Heavy metals are naturally occurring metallic element that exhibited relatively high specific gravity then water and is extremely toxic or poisonous at low concentrations [1, 2, 3] . Some of these are essential metals, such as iron, copper, zinc and manganese, which have significant biological roles as cofactors for various enzymes and proteins while as others have no biological role but are poisonous, e.g., mercury, lead and cadmium [4] . The amount of heavy metals in industrial leachates is of great concern as these chemicals are present in large quantities and are continuously discharged into aquatic ecosystem [5, 6] . Due to their toxicity, persistence and bioaccumulation potentials, heavy metals are considered as one of the most significant aquatic pollutants [7] . Among these heavy metals, lead is a non-essential metal that occurs naturally in nature. On the other hand, anthropogenic activities also increased its concentration in the natural environment [6, 8] . Lead is a persistent metal [9] , has slow elimination rate therefore, accumulated in the fish body [10, 11] , via respiration, adsorption and oral ingestion through the food chain [12, 13, 14] . The main objective of the environmental toxicologist is to assess the risk resulting from the presence of such substances. Fish have been used for many years to determine the pollution status of water and are thus considered as excellent biological indicator in aquatic ecosystems [15, 16] . As the exotic fishes are considered to be very hardy, most adaptable and have high reproductive potential, hence these are immune to such toxic substances present in the water. Therefore, in the present study, Ctenopharyngodon idellus (grass carp) has been selected as the test animal. They are ideally suitable for laboratory conditions for longer periods. Scanning electron microscope is a valuable tool for evaluating the toxic effects of environmental pollution on fish structures that are vital for their fitness or survival [17] . Limited studies on surface morphology have been reported on the scales of fish treated with heavy metal using scanning electron microscope (SEM). Hence, in the present study, it was decided to determine the ultrastructural deformities induced on the scales of C. idellus treated with sublethal concentrations of lead nitrate by SEM.