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Effect of the water exchange rate in a recirculation aquaculture system on growth, glucose and cortisol levels in Oreochromis niloticus

In recirculating aquaculture systems (RAS), the water exchange rate influences the removal of waste compounds. However, the inappropriate exchange rate favors the presence of stress factors, causing alterations in the cultured organisms. Therefore, the aim was to determine the effect of the water exchange rate in the different productive stages (fingerling, juvenile, and adult) of Nile tilapia (Oreochromis niloticus). Three exchange rates were used: rates of 1.2 (T1), 2.8 (T2), and 5.3 (T3) tank volume h-1. The following were established as response variables: growth rate (GR), survival rate (SR), feed conversion rate, protein efficiency, and condition factor. Likewise, cortisol and glucose concentrations were established as explanatory variables. The results suggest that in the fingerling stage, the T2 treatment contributes most to the productive performance (GR = 40.24 g and SR = 95%), keeping low levels of cortisol and glucose (6.76 ng mL-1 and 33.73 mg dL-1). In the juvenile stage, T3 treatment shows the best result both in productive performance (GR = 117.69 g and SR = 90%) and in cortisol and glucose concentrations (35.13 ng mL-1 and 70.67 mg dL-1). Finally, all treatments present cortisol and glucose levels above the normal range in the adult stage, T1, where the highest productive performance is presented (GR = 90.06 g and SR = 95%). The information leads us to consider the variation in the exchange rate in a RAS through the different stages of the Nile tilapia to maintain the favorable conditions that lead to the highest performance.