Salinity and temperature effects on the lipid composition of mullet sea fry (Mugil cephalus, Linne, 1758)

A large part of the extensive aquaculture in Tunisia was based on the transfer of mullet fry from the marine coastal areas to the continental fresh water lakes, the aim of this work is the monitoring of the changes made in the lipid composition of Mugil cephalus fry according to salinity and temperature acclimation. Fish acclimated to 14 degreesC and 0.5 psu salinity, contained 55% less total fatty acid than those acclimated to the seawater at the same temperature. Low salinity induces an increase in the percentage of some polyunsaturated fatty acid such as the 22: 5 (n - 3), the 22: 6 (n - 3) and the 20: 4 (n - 6), as a result of change in the level of triacylglycerol content or the activation in the synthesis of those fatty acids. The transition of the acclimation temperature from 26 to 14 degreesC in seawater is followed by a 215% increase in the amount of total fatty acids in the fourth week of acclimation. The total fatty acid levels of all fish at 1 week were higher than most values at 4 weeks. There was an increase of polyunsaturated fatty acids percentages due to the decrease of the temperature at the low salinity. We conclude that the changes made in the salinity and temperature of acclimation, are followed by a quantitative and qualitative variation in the lipids of M. cephalus fry. The decrease of these two parameters offers an improvement of the synthesis of the polyunsaturated fatty acid from the 18 carbon unsaturated precursors in M. cephalus fry.