Salinity and temperature effects on some haematological parameters and plasma osmolality of fasted yellow eel, Anguilla anguilla/ Effets de la salinite et de la temperature sur les parametres hematologiques et sur l'osmolalite plasmatique de l'anguille jaune, Anguilla anguilla maintenue a jeun

The responses of haematological parameters and plasma osmolality to variations in temperature and salinity were followed for the European eel [Anguilla anguilla (Linnaeus, 1758)] at yellow stage. Fish were maintained under food deprivation and experimented environmental variations that they are susceptible to face during their continental life and at silver stage during their migratory way. The number of red blood cells, haematocrit, haemoglobin concentration and plasma osmolality were determined. Erythrocytes parameters were also calculated: mean corpuscular volume, mean corpuscular haemoglobin concentration and mean corpuscular haemoglobin. Yellow eels were captured in the Gulf of Tunis and then maintained in the laboratory either in freshwater (0.5 %o) or seawater (35 %o) at low (4°C), ambient (16-18°C) and high (28°C) temperature. Haematological parameters and plasma osmolality were evaluated after 30 and 60 days of experiment. All haematological parameters were stable under variations of salinity. At high temperature, the number of red blood cells increased significantly in freshwater and seawater without influencing the erythrocytes constant values indicating a stability of the physiological state of yellow eels under thermal stress. During the yellow stage, the European eel has a strong capacity to adapt and to stabilize the values of haematological parameters that are usually used to indicate physiological fish disturbance. Plasma osmolality of yellow eels acclimated in seawater was higher than those acclimated in freshwater conditions for all experimental conditions. Fasting caused an increase in plasma osmolality in seawater, while no significant variations were observed in freshwater. Low and high temperature also increased plasma osmolality in freshwater and seawater compared to ambient temperature. This variability in plasma osmolality due to fasting, salinity, and temperature variations depends on the osmotic regulation, which controls the ionic composition and the organic content of plasma. This study shows that the fasted yellow eel has no difficulty to cope with salinity and temperature changes due to the regulation of haematological parameters and plasma osmolality. Key words Anguillidae Anguilla anguilla Haematology Osmolality Salinity Temperature Fasting Les reponses de certains parametres hematologiques et plasmatiques ont ete suivies pour l'anguille europeenne de stade jaune [Anguilla anguilla (Linnaeus, 1758)] maintenue a jeun et acc