Feed Digestion, Growth and Disease Prevalence in Nile Tilapia (Oreochromis niloticus) Cultured at Different Water Exchange Rates in a Recirculating Aquaculture System

The quality of culture water and the rate of water flow within a culture system can affect fish growth and health. In this study, the effects of different water flow rates on digestion efficiency, growth and welfare of juvenile Nile tilapia (Oreochromis niloticus) (Initial weight: 25.75±0.47 g) were investigated. Fish (15 per tank) were randomly stocked into twelve 150 L thermoplastic tanks of a recirculating aquaculture system and subjected in quadruplicate groups to water flow rates of 50 Lh-1 (Low exchange; LE), 100 Lh-1 (Medium exchange; ME) and 150 Lh-1 (High exchange; HE) for 72 days. Water quality parameters including total ammonia nitrogen, nitrate and alkalinity, dry matter, protein and lipid digestibilities, somatic growth and some welfare indicators including haematology and disease prevelance were monitored. There were no significant differences in growth among the treatments. Higher prevalence of cataract, fin erosion, oral and dermal lesions were observed in the LE and ME treatments indicating compromised welfare. There were no statistical differences among the treatments in terms of nutrient digestibility. This study has shown that culturing Nile tilapia under moderately high water flow rates of at least 100% tank water replacement per hour in RAS ensures good growth and feed utilization.