The effect of heavy metal, arsenic on changes in total oxygen consumption at different sublethal concentration and
different time intervals of 10, 20 and 30 days was studied in a fresh water teleostean cat fish, Mystus vittatus (Bloch). The average oxygen consumption by this fish in normal water was 0.614 ml/g/hr in control. The glycogen, protein, triglyceride, acid and alkaline phosphatases content were decreased 21.49–61.78%, 11.56–47.22%, 14.76–65.05%,
7.98–54.35% and 16.67–38.71%, respectively in arsenic exposed fish. A significant decreased in oxygen consumption and organic reserves of gills were recorded at every time and every concentration of arsenic trioxide as compared to control fishes. The effect was more pronounced as the concentration of arsenic trioxide and duration of exposure
increased.Keywords: Arsenic; Gill; Glycogen; Mystus vittatus; Oxygen consumption; Protein; Triglyceride.