Oxygen consumption and ammonia excretion in different size groups of clam, Marcia opima collected from
Tuticorin Bay in Tamil Nadu was studied. Oxygen: Nitrogen ratio was calculated by using atomic equivalents
and ranged between 133 - 175 for small, 97 – 117.2 for medium and 63.5 – 75.8 for large clams on day one.
After day 3, the range was 238.4 – 282.1, 160.9 – 189 and 100 - 137.5 respectively. During starvation, a
decline in excretion rate has been observed, which can be proposed as an index of stress. The study supports
interaction of oxygen consumption and nitrogen excretion, which can provide a better understanding of the
oxidative and nitrogen metabolism in the clam.