Etude de la tolérance a la température et a la salinité chez le Tilapia du Nil Oreochromis niloticus (l.) élevé dans les eaux geothermales du sud Tunisien

Abstract

The present study aims to investigate temperature and salinity tolerance of tilapia, Oreochromis niloticus, under controlled laboratory conditions. This by exposing fish to high temperatures and salinities in order to determine their tolerance to these factors. The effect of body size and acclimation temperature on the lethal temperature (LT) of Oreochromis niloticus is investigated after 10 days acclimation period at 20 'C and 30 'C . Indexes used as practical measures of tolerance temperature are: mean survival time (MST), defined as the mean survival time over 24h, 48h and 72h period, and lethal temperature (LT sub(50)) 24, 48, and 72h defined as the temperature at which survival falls to 50% after 24h, 48h, and 72h. For the first acclimation (20 'C), the LT sub(50) were 40.12 'C , 38.35 'C and 36.59 'C respectively for 24, 48 and 72h. For the second one (30 'C), these limits were 40.73 'C, 38.82 'C and 36.92 'C. No significant effect of body size on temperature tolerance was observed. Compared to other teleostei, this species presented a wide range of temperature tolerance. Despite it's freshwater fish behavior, Oreochromis niloticus shows a high salinity tolerance (28g l super(-1)). Otherwise, results show that salinity tolerance was closely related to size and maximum tolerance may be acquired at a total body length of approximately 6cm and remained relatively unchanged beyond this length.