UTTAR PRADESH JOURNAL OF ZOOLOGY

Background: Cadmium (Cd) is a persistent, non-essential heavy metal that enters aquatic ecosystems through industrial, agricultural, and urban effluents, posing a severe threat to freshwater fish. Channa gachua (Hamilton), a facultative air-breathing snakehead widely distributed across South and Southeast Asian wetlands, is repeatedly exposed to surface-water contaminants owing to its aerial respiration behaviour, yet no published study has determined the acute toxicity of cadmium chloride (CdCl₂) in this species. Methods: A static-renewal 96-h acute toxicity bioassay was conducted using five nominal CdCl₂ concentrations (28, 30, 32, 34 and 36 mg/L) in triplicate, with 10 fish per replicate aquarium (30 fish per concentration). Mortality was recorded at 24, 48, 72 and 96 h, and median lethal concentrations (LC50) were estimated by Finney’s probit method (Finney, 1971). Behavioural and morphological alterations were monitored qualitatively throughout the exposure period, and representative photographs were recorded. Results: Mortality increased in a clear concentration- and time-dependent manner. The 96-h LC50 was estimated at 28.8 mg/L (regression: y = −18.82 + 16.32x; log-probit basis), with LC50 declining progressively from 38.7 mg/L (24 h, extrapolated) to 34.1 mg/L (48 h) and 31.5 mg/L (72 h). Exposed fish showed concentration-dependent behavioural disturbances consistent with those reported for the congener Channa punctatus. Conclusion: Channa gachua displays a clear dose- and time-dependent acute toxicity response to CdCl₂, with a 96-h LC50 of 28.8 mg/L, which is positioned within the wide 6.19–80.62 mg/L range reported across independent congeneric determinations for Channa punctata, reflecting both genuine interspecific variation and substantial methodological heterogeneity in the existing literature that merits further controlled, side-by-side investigation.