Commercial aquaculture is growing worldwide. With fisheries reaching a stagnating phase, India will have to look to aquaculture in different way, in the future to provide fish products that will likely be needed. In view of this, a study on water quality management was done which specifically looked at the effects of dissolved oxygen (DO) on fish population growth and increase of body mass. The study was done by using Molly (Poecilia sphenops) in fresh water habitat. In the case study, 120 molly of 0.5 - 1 g. in weight were reared in replicate at 40%-100% DO levels in different aquarium of 10 liter capacity. Every alternate day 5 gm of food was given. The DO was regularly measured by Wrinkler’s method. The subsequent effect of oxygen saturation levels on growth and feed conversion ratios were taken in three, six, nine and twelve months. The results showed that oxygen saturation level had an effect on the reproduction, growth and food conversion ratio. Below 60%, the population growth was comparatively lower. Feed conversion ratio was higher at 60% and above, compared to lower oxygen level. However it is found that at highest DO level the body mass increase is little lower than medium DO level (75.1%). The rate of population increase is highest at DO 88 % but the body mass increase is little lower (91%) in that DO. The conclusion is that oxygen saturation level has a positive correlation with population growth and food conversion to body mass ratios of fish. But at high DO condition the fish probably increase its activity and metabolism.

Keywords: Dissolve Oxygen; Fish; FCR; Molly; Physiology; Respiration