Lipid distribution and composition in Antarctic toothfish before and after reproductive migration: implications for the life cycle

Six Antarctic toothfish (Dissostichusmawsoni) have been analyzed for qualitative and quantitative determination of muscular lipid distribution. The specimens were representative of different physical condition and life stage: two adults in good condition and two adults in poor condition (termed "axe handles" based on their emaciated shape) from the spawning area of the Ross Sea seamounts, and two sub-adults from the continental shelf. Axe handles had lower lipid quantities. Among the individuals in good condition, adults from the seamounts had higher accumulation of lipid in the dorsal portion, maybe related to the neutral buoyancy for the reproductive migration. Thirteen saturated fatty acids (SFA) and three unsaturated fatty acids (UFA) have been identified. Subadults from the shelf had higher SFA/UFA ratios in the anterior part of the body, where they might store somatic lipids for buoyancy. The individuals from the spawning area had higher SFA/UFA ratios in the posterior part of the trunk, indicating after the migration a primary consumption of the somatic fatty acids near the center of buoyancy. SFA uptake from the diet seems to be difficult at the spawning area and they may be replaced by UFA. This translates into a reduced ability to re-acquire neutral buoyancy for a returning migration.