Effect of Chromium Trivalent (Cr-Iii) And Hexavalent (Cr-Vi) Toxicity on The Morphology of Zebra Fish, Danio Rerio (F. Hamilton, 1822) During Early Embryonic Developmental Stages

Chromium is very often considered as a pollutant that threats aquatic ecosystems. The aim of the present study deals with the acute toxicity and its effects of chromium trivalent (Cr-III) and hexavalent (Cr-VI) on zebra fish, Danio rerio embryo. As per OECD guideline for Fish Embryo toxicity Test (FET), from blastula stage to hatching was developed. Embryo assay indicated the lethal (LC99), median  lethal (LC50) and sub lethal (LC1) concentrations of chromium (Cr-III and Cr-VI) were 101.89, 77.72, 59.29 mg/l and 14.29, 13.43,12.62 mg/l respectively. Based on LC50 values, embryos were exposed at low (20 mg/l), mid (30 mg/l) and high (45mg/l) concentrations of Cr-III and the other three concentrations low (6 mg/l), mid (7.2 mg/l) and high (8.64 mg/l) of Cr-VI. FET carried out during 24, 48, 72 and 96 hrs after exposure of chromium indicated with weak pigmentation, edematous yolk sac, weakened skeleton, lordoris, pericardial edema (Poe), delayed hatching and shortened tail. Significant reductions of embryonic eye development, embryo movements, heart beats and short tail length were noticed. This study reveals the occurrence of developmental toxicity in the embryo stages and it could be correlated to the generation of oxidative stress. The reduction of embryo movements and abnormal swimming of newly hatched larva indicates neurotoxicity. This study proves the Cr-VI (chromium hexavalent) metal threats  to aquatic organism, and affects the food chain as well as human beings. This assessment can be a valid biomarker in aquatic toxicology to emphasize the limited usage of chromium metals.