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Increasing stocking densities affect hemato-immunological parameters of Nile tilapia reared in an integrated system with Pacific white shrimp using biofloc technology

Highlights•The highest fish stocking density increased hematocrit and total leukocyte count.•The two highest densities resulted in higher neutrophil and agglutination titer.•Results suggest that fish were not characterized by general immunossupression.•Immunoenhancement seems to have occurred towards the end of the trial.AbstractThe aim of this study was to investigate the effect on fish health indicators of different Nile tilapia (Oreochromis niloticus) stocking densities when reared in an integrated culture with Pacific white shrimp (Litopenaeus vannamei) using biofloc technology for 57 days. Three fish densities were evaluated: 8, 16 and 24 fish tank−1 with four replicates each. The experimental units comprised 800 L (useful volume) tanks for shrimp rearing and 90 L (useful volume) tanks for the culture of tilapia, which had an initial mean weight of 9.64 ± 0.14 g. A submerged pump located inside the shrimp tanks recirculated the water between the two units. The system was managed as a biofloc technology unit, with the addition of organic carbon to control ammonia and the monitoring of water quality, which remained within suitable ranges for both species. On day 57, fish were sampled for the assessment of the hemato-immunological variables. Fish reared under the highest stocking density exhibited significantly higher values of hematocrit and total leukocytes when compared to the two lowest densities (p < 0.05). The count of neutrophils and the agglutination titer were significantly greater in the 16 and 24 fish tank−1 groups (p < 0.05). These results suggest that, although the fish reared under the two stocking densities appear to have been undergoing physiological changes at the end of the culture period, the hemato-immunological alterations were not characterized by a general immunosuppressed state and instead by immunoenhancement. This is an indication that the carrying capacity of the system as regards fish density was being reached only towards the end of the trial.

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