Hematology of Nile tilapia fed supplementation with algae challenged by acute and chronic stress

The aim of this trial was to evaluate hematological parameters of tilapia Oreochromis niloticus fed diet supplemented with ergosan, an algae product, in a chronic and acute stress challenge. The experiment was carried out with juvenile tilapias Oreochromis niloticus (15g), in 500 L-tanks linked at a water recirculation system, with constant water flow and controlled temperature, stoking 35 fish/tank. Fish were fed test-diets during 10 days and, at the end of this period, received a diet without supplementation, when they were submitted to chronic and acute stress challenge. Fish were distributed in a completely randomized design, in a factorial scheme 4x2: four supplement levels (0; 0.25; 0.5 and 1% supplement in the diet) with two stresses (chronic and acute). Results showed the stress stimulus applied were able to induce physiologic changes on fish, including reduction of erythrocytes, erythroblasts and leucocytes number and increasing medium corpuscular volume. Oral administration of 1% supplement during 10 days for Nile tilapia juveniles under acute stress induces a higher thrombocyte number (69%) in the blood.