Skin, red and white muscle, belly flap, dorsal fat depot, backbone, head, visceral tissue and liver of commercially farmed Atlantic salmon (Salmo salar) were analysed for total lipid content, lipid classes and fatty acid composition. The fat is deposited in a number of tissues and organs with the highest level in the dorsal fat depot (38.4% of wet weight), red muscle (27.2%) and belly flap (28.1%). The fat content in white muscle is 9.6% of wet weight. The lipid class distribution is nearly uniform throughout the fish body. The belly flap contains the highest amount of triacylglycerols (98.8% of total lipid) and white muscle and visceral tissue have the lowest levels, 93.3% and 93.1%, respectively. The variation in total saturates, monoenes, polyenes, n-6 and n-3 fatty acids was much less between tissues than the variation in total lipid content. In the edible part, the belly flap (16.7%) contained significantly lower levels of n-3 fatty acids than red (18.4%) and white muscle (19.7%) mainly due to lower level of 22 : 6n-3 and 20 : 51-3 fatty acids.

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SUMMARYWhen the NaCl concentration of a suspension of Halobacterium salinarium is gradually lowered by adding water, the rod-shaped organisms are converted to spheres which lyse. The organisms do not change in size when transformed from rods to spheres. Chemicals which do not possess a strong net charge in aqueous solutions do not protect the structure of the organism when they replace NaCl in iso-osmolar concentions. The rod shape of the organisms is only maintained by very high concentrations of ions which interact weakly with common proteins; lithium and ammonium ions are exceptions to this rule. Ions which display strong interactions with common proteins, and chemicals which are believed to break secondary bonds between protein molecules, effect a transformation of rods to spheres, and frequently a lysis of the spheres, when brought in contact with organisms suspended in strong NaCl solution. The changes in structure in hypotonic and isotonic solutions are not affected by metabolic inhibitors. Isolated cell-wall fragments disintegrate into smaller units when exposed to conditions under which whole organisms lyse. It is concluded that the structural transformations and lysis of H . salinarium in hypotonic solutions are not caused by the action of enzymes and that osmotic phenomena play no, or only a minor, role. The observations support the contention that the globular lipoprotein particles, which constitute the bulk of the material of the cell wall of these bacteria, are bound together mainly by electrostatic forces and secondary bonds. When the cells are exposed to hypotonic solutions, or to ions which bind strongly to proteins, or to chemicals which are believed to break secondary bonds between protein molecules, the linkages binding the lipoprotein particles together are weakened so that the wall structure disintegrates. Only in the presence of high concentrations of sodium and chloride ions, or other ions which bind loosely to proteins, is it possible for the proteinaceous particles of the cell wall to associate in an orderly array.

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