UTTAR PRADESH JOURNAL OF ZOOLOGY

Fish is a dietary staple across North-East India, and the three species that dominate consumption and trade in the region are catla, rohu and hilsa. The Brahmaputra and Barak river systems, their associated floodplain wetlands and the adjoining hill catchments carry a well-documented burden of geogenic arsenic, mining-derived acidity and metals, and urban and industrial effluent, which has generated a widespread assumption that these three species carry correspondingly elevated tissue burdens of toxic metals. This review examines whether that assumption is supported. The available literature was appraised critically rather than catalogued, with attention to what has actually been measured in fish tissue within the region, what has been measured only in water, sediment, soil or groundwater, and what has been imported from other species or other river basins. The regional evidence proves to be strikingly asymmetric. Contaminant pressure in the abiotic compartments is documented in considerable detail across the Brahmaputra floodplain, the Guwahati urban corridor, the Meghalaya coal belts and several floodplain lakes, yet direct tissue measurements for the three target species are almost absent, amounting for practical purposes to a single dataset for rohu from one polluted river in central Assam. No verified tissue dataset for catla or for hilsa captured within North-East India was retrieved. Statements about bioaccumulation in these species in the region therefore rest on three successive extrapolations, from abiotic concentrations to biotic burdens, from surrogate species to target species, and from other basins to the Brahmaputra and Barak systems. Each of these links is shown to be weaker than the confident tone of much of the applied literature implies, because uptake is governed by bioavailability and speciation rather than by total ambient concentration, because feeding guild and vertical niche differ sharply among the three species, and because the contaminant signature of the Brahmaputra floodplain is dominated by geogenic arsenic in a way that Gangetic and Bangladeshi comparators are not. Anadromy makes hilsa a distinct case, since tissue burdens integrate marine, estuarine and riverine exposure and the provenance of hilsa sold in regional markets is largely undocumented. Recurrent methodological weaknesses further constrain inference: inconsistent reporting of wet or dry mass, sparse quality-assurance documentation, neglect of arsenic speciation, absence of size and age standardisation, and risk calculations parameterised with consumption rates that are unlikely to describe North-East Indian diets. The most defensible conclusion is that regional risk remains undetermined rather than demonstrated to be either acceptable or unacceptable, and that species-resolved, speciation-aware and provenance-aware monitoring is the necessary next step.