No Distinct Sexual Dimorphism
According to researchers at the University of Toronto and Laurentian University, the lake trout is the only salmonid that does not display sexual dimorphism, such as distinctive body color differences or snout differences. However, other sources note small physical differences between males and females.
Physical Markings
Although the coloration and appearance of lake trout can vary depending on habitat, season and between populations, male lake trout will have a slightly longer snout than females. Additionally, males will develop dark horizontal bands on their sides, as well as dark areas around their heads. Also, the top portion of the bodies of male lake trout will be paler than females'.
Spawning Habits
During spawning season, male lake trout will reach the spawning area well in advance of the females. Courtship may proceed as follows: the female lake trout will swim in large circles around the spawning area, followed by one to seven male lake trout. Two males at this point might nudge her with their snouts, swimming alongside her on opposite sides. As they quiver, she may drop to the bottom, in which case the quivering males will drop also. At the bottom, the female will either keep swimming or spawn. Prior to spawning, she will quiver, to which the males will respond by releasing gametes.
Territoriality and Competitiveness
Unlike other salmonids, female lake trout do not build nests and instead lay their eggs sporadically over the course of large areas. They do not exhibit territoriality in defending or upholding these areas. Male lake trout also do not vie with each other competitively, as other male salmonids do.