Chalakudy River is the fifth longest river in Kerala with a total length of 144 km which supports rich fish diversity. An unidentified rare mahseer species of the Chalakudy river is a red variety locally known as 'choppan choora' (choppan=red;choora=mahseer) is not eaten by the people as its consumption leads to giddiness, nausea and vomiting which last for at least 24 hours. The present study describes the toxic factor present in Tor sp. of Chalakudy River. Bioassay-guided fractionation was

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... loyed to identify the active compounds from fish sample. Purification of the crude extract was done by Gel filteration chromatography on a Sephadex G-100 column. Spectrophotometric analysis of Tor sp. showed highest peaks as compared to the Tor khudree. Water sample analysis of toxic cyanobacteria showed negative result by PCR. Preliminary studies on mouse Bioassay was carried out at Central Institute of Fishery Technology (CIFT), Kochi. The animals were observed for signs of toxicity for 24 hr after dosing for 2 days. Fraction showed mild symptoms in Aqueous extract at 0.6ml dose. Intraperitoneal mice study was conducted at Kerala Veterinary and Animal Sciences University (KVASU), Thrissur for 2 days. Mice exhibited lethality within 24hr. It can be assumed that the current toxin might be a proteinaceous compound. Control was maintained throughout the study from nontoxic Tor sp. (Tor khudree). Further studies are needed for exactly characterizing the toxic factor and follow up its course of biochemical pathways.