Recirculating aquaculture systems affects hematological parameters and increases ectoparasite susceptibility in Nile tilapia Oreochromis niloticus

We herein evaluated the hematology and parasitology of Nile tilapia previously raised in an earthen pond and transferred to a recirculating aquaculture system (RAS) to verify any possible influence of RAS on such health parameters. For this, 780 tilapias with an initial average weight and length of 91.05 ± 27.08 g and 17.45 ± 1.91 cm, respectively, were distributed in three tanks (2.0 m3) attached to the RAS, where they remained for 54 d. Throughout the period, water quality parameters remained within the range suitable for the cultivation of the species. Tilapia growth performance was satisfactory in the RAS, reaching a final biomass of close to 300 kg and survival of 98%. Hematological and parasitological analyses at the end of 54 d showed possible stress in RAS, with a significant increase in neutrophils from 12.15 ± 6.66 (earthen pond) to 21.43 ± 11.68% (RAS) and erythrocytes from 1.81 ± 0.24 (earthen pond) to 2.13 ± 0.14 (RAS), and a significant decrease in lymphocytes from 22.4 ± 2.66 (earthen pond) to 13.67 ± 3.38 (RAS). Furthermore, parasitological analysis showed a significant increase in the number of parasitized fish (25% to 63%) and abundance (3.55 ± 6.44 to 9.37 ± 9.99) after 54 d. It was concluded that tilapia cultivation in RAS can cause hematological changes and increase parasitism.