The adaptations of aquatic organisms to high latitudes are primarily concerned with an adjustment to low temperatures and seasonal changes in illumination, including an alteration of Polar Night and Day. The adaptations always involve multiple aspects and levels – from the molecular to the behavioral. The most important adaptations to low temperatures are: the movement of water from the intracellular to the extracellular compartments, so that the molecular weight of the intracellular fluid increases and its freezing point shifts downwards, preventing an intracellular freezing, ensured by the synthesis of anti-freeze compounds; the transition from saturated to unsaturated fatty acids, which is a critical mechanism for the membrane lipids functioning; as well as the synthesis of more flexible proteins. The most crucial component of the algae adaptation is their variable thermal resistance and an increase in the content of photosynthetic pigments as the daylight duration decreases. The reserves necessary for survival during the Polar Night are accumulated in the summer season. Cryoflora adaptations are studied. Some essential adaptations occur in oogenesis. The synthesis of fats in the yolk increases considerably, enabling a transition from the primitive ontogeny in the larval stage to a more advanced, direct ontogeny, which meets the conditions of high latitudes better. An asynchronous type of oogenesis remains during the transition from a repeat to single spawning.