Abstract: Twenty-five fresh water “Thaila”, Catla catla of various sizes were sampled from Korang River Islamabad, to study the parameters of weight-length and condition factor. Log transformed regression were used to test the allometric growth. It was observed that growth in weight is almost proportional to the cube of its length. The value of slope b = 3.05 coincides with the slope of that of an ideal fish. Condition factor remains fairly constant with increasing length or weight. The predictive equation can be used to estimate parameters investigated with a fair amount of accuracy with in the size range studies.