The effects of low salinity on lipid composition in the gills of grey mullet "Liza ramada"

Abstract

Thin-lipped grey mullet Liza ramada adapted to sea water (SW, 35ppt) were submitted to abrupt osmotic stress by transferring the specimens to Freshwater (FW, 0.5 ppt) for 24 hours. The adaptation capabilities of Liza ramada were evaluated using parameters such as osmolality, blood hematocrit and red blood cells. Variations of fatty acid composition in the gills of the thin lipped grey mullet liza ramada subjected to direct exposure to freshwater were determined. The plasma osmolality, blood hematocrit and red blood cells decreased within the first 24 h. There were quantitative and qualitative differences between the fatty acids composition of Liza ramada gill in response to the media salinity. The monounsaturated fatty acids (MUFA), particularly oleic acid C18:1(n- 9) increase at lower salinity. The polyunsaturated fatty acids (PUFA) decreased with decreasing salinity due primarily to changes in n-3 PUFA especially C18:4(n-3), C20: 5(n-3), C22: 5(n-3) and C22: 6(n-3).Higher linoleic acid C18:2(n-6) content observed in fresh water fish was accompanied by a significant decrease of arachidonic acid C20:4(n-6