Effects of an experimental challenge with Mycobacterium marinum on the blood parameters of Nile tilapia, Oreochromis niloticus (Linnaeus, 1757)

Abstract

A hundred adult of tilapia, Oreochromis niloticus, were inoculated intraperitoneally with 10(8) c.f.u. of Mycobacterium marinum. Other 100 speciemns were maintained without inoculation. Blood samples of six inoculated animals were collected at 01, 03, 07, 14, 21, 28, 35, 42, 49, 56 and 84 days after inoculation. Initially, six specimens were taken from the non inoculated group ("time zero"). The haematological parameters determined were: haematocrit (Hct), haemoglobin concentration (Hgb), total erythrocytes count (RBC), hematological indexes (MCV, MCH and MCHC), thrombocyte count (Tr), leukocyte count (WBC) and leukocyte differential count. There were no changes in Hct, Hgb, MCH and MCHC. However, the mean values for RBC and MCV decreased. The mean values for RBC and Hct of specimens from the "time zero" group were higher and the MCV and MCH lower than in inoculated animals. Occurred neutrophilia, and, at 72 h there was lymphocytosis and neutropenia. By the 49th day after bacterial inoculation, there was monocytosis.