Fish is a major and cheaper source of animal protein and its sustainable production has been limited to aquaculture as capture fisheries has been levelled-off for almost three decades now. However, expansion of aquaculture is being challenged by resources among which water is a major one. There are different methods of culturing fish and one of the most commonly used in tank systems is stagnant-renewal method where water is changed frequently to keep the fish at optimal performance. This is mostly done arbitrarily and sometimes rely on the visual appearance of the culture water. There is limited information on how often the water changes should be conducted. This research examined the effect of water changing frequency on two major fish species cultured in Nigeria and Africa, Nile tilapia, Oreochromis niloticus and African catfish, Clarias gariepinus. The experimented water changing frequency was 50% at two days interval, four days interval and once in a week. The results showed that water change once a week is adequate for fish stocked between 10 kg/m3 and 20 kg/m3. The water quality parameters were all within the recommended range for tropical fish culture, and only a few parameters like total dissolved solids and electrical conductivity were significantly different among the treatments. The growth performance and nutrient utilization parameters were similar in O. niloticus. In C. gariepinus, frequency of water change influenced the growth and nutrient utilization parameter, with performance increases with increased number of days of changing the water.
While further research is suggested, changing of culture water once a week is established to support improved growth performance, nutrient utilisation and well being of the fish culture. This, if adopted will reduce water usage in fish culture and increased fish production despite reduced labour and environmental friendly as the frequency of waste discharge is reduced