Changes in astaxanthin and fatty acid concentrations during the developmental process in the calanoid Arctodiaptomus walterianus in an alpine lake at low latitudes

Astaxanthin is ubiquitous in calanoid copepods in high latitude or altitude regions and is well studied. However, the dynamics of astaxanthin in calanoids at low latitudes are less studied. We collected samples during the ice-free season from Lake Mubanghai, an alpine lake located in a low-latitude and high-altitude region, and analyzed astaxanthin content changes among different developmental stages in Arctodiaptomus walterianus. The total astaxanthin content in A. walterianus varied from 1.66 to 4.49 mu g/mg dry weight and was highest in October, the month with the lowest temperature among the three sampling dates. Both free astaxanthin and astaxanthin esters content per biomass and the ratio of free astaxanthin increased from the nauplius to adult stage, and astaxanthin esters dominated in total astaxanthin in all developmental stages. The concentrations of polyunsaturated fatty acids were low in seston but were the main fatty acids in the calanoid. The total fatty acid concentration was positively correlated with the concentrations of total astaxanthin, free astaxanthin and astaxanthin esters in the calanoid. These results suggested that astaxanthin may be beneficial to the accumulation of fatty acids. This strategy may benefit calanoids in adaptation to high mountain environments at low latitudes.