D espite M. relicta' s somewhat unclear history, its importance of in aquatic food chains is well documented and has become of particular interest to many fisheries managers of cold water lakes. In the past 70 years the natural distribution of M. relicta has been increased by its introduction into freshwater lakes as an addition to the forage base of sport fisheries. The specie's distribution is limited by its habitat requirements, which include cold, deep, oligotrophic, well-oxygenated waters. Mysids have a thinner carapace that does not completely cover the thorax, and walking legs are replaced with long, thin, setose appendages used for swimming, feeding, and respiration. The first two pairs of appendages are used for raptorial zooplankton feeding or straining phytoplankton and particulate debris.
Respiration occurs through the thin carapace which is most efficient during swimming and feeding.
The stalked eyes are large, compound, and well developed for precise photoreception. Mature males can be distinguished by their abnormally long and specialized fourth pleopod which is the gonopod. Mature females develop a brood pouch at the base of the last pair of legs, and generally reach larger sizes and are more abundant. Vertical Migration O ne of the more salient features of M. relicta's life history is its vertical migration. Generally, they migrate to the metalimnion when light levels decrease at dusk and then return to deeper waters with the increasing light levels at dawn.