Changes of major carotenoids in gonads of sea urchins (Strongylocentrotus intermedius and S. nudus) at maturation. Changes in the carotenoid content in gonads of two sea urchins species were investigated during maturation. The content of echinenones and carotenes, the two major carotenoid fractions in gonads, is highest for Strongylocentrotus intermedius at the spawning gametogenic stage of gonad maturation for both sexes. For S. nudus, the content of these pigments is highest at stages of active gametogenesis and spawning for males and at the growth stage for females. A comparison of the carotenoid content dynamics during maturation of gonads for males, females and animals at the resting (sexual inactivity) stage was also carried out.