Red blood cell parameters and osmotic fragility curve of Colossoma macropomum (Pisces, Osteichthyes, Mileinae) in captivity

Abstract

In order to establish reference values for certain haematological parameters and osmotic fragility curve for the blood of Colossoma macropomum, blood samples were collected from 38 fish bred on farms in the state of Tocantins, Brazil. Red blood cell count, haemoglobin content and haematocrit were determined. Osmotic fragility curves were determined for 30 minutes under resting conditions at 30ºC, incubated curves at 37, 30 and 27ºC for 24 hours and incubated curves for 12 hours at 27ºC. The haematimetric values obtained were: red blood cell count= 1.58 ± 0.08 x10¹²/L; haemoglobin= 7.2 ± 0.32 g/dL; haematocrit= 34.0 ± 1.6%; MCV= 217.6 ± 13.2fL; MCH= 46.3 ± 2.6 pg and MCHC= 21.5 ± 1.4%. Osmotic fragility of fish erythrocytes was assessed according to haemolysis rate. Haemolysis began at 85.5 mM NaCl and total haemolysis occurred at 17 mM NaCl. Samples from incubated curve for 24 hours showed total haemolysis in all concentrations, regardless of temperature. In the samples from incubated curve at 27ºC for 12 hours initial haemolysis was observed at 154 mM and total haemolysis at 17 mM NaCl