Measurements of oxygen consumption and ammonia excretion were made from different size groups of green mussel, Perna viridis collected from Ratnagiri coast in Maharashtra. Oxygen: Nitrogen ratios were calculated by atomic equivalents and ranged between 57.5 and 96.5 for small, 80 and 86 for medium and 80 and 85 for large mussels on day 1, but after day 3,116.2- 120.5, 101.1 - 105.5 and 77.7 - 84.4 for the above respective groups. Decline in excretion rate during starvation, has been proposed as an index of stress. The study supports interaction of oxygen consumption and nitrogen excretion, which help in understanding oxidative and nitrogen metabolism of the animal.