Mechanisms of homing in salmonids

Abstract

The article reviews modern concepts of the significance and mechanisms of homing and its complementary straying in salmonids. Homing is a fundamental, highly adaptive characteristic of salmon behavior. An intraspecific population structure formed in salmon on its basis, and it includes a great number of reproductively isolated populations, among which a small-scale migration is possible via straying. Straying allows salmon to colonize new habitats and recolonize empty ones after extinction of the local populations. The homing ability became the basis for large-scale artificial salmon reproduction. The following physiological mechanisms of homing are considered: the primary role of olfaction and the process of sequential imprinting of olfactory stimuli of a natal river which occurs in juveniles, mainly during the smoltification period, as well as in the earlier stages of life and during downstream migration; the use of olfactory “memory” by adult fish returning to spawn; the role of hormonal regulation in the imprinting process in juveniles and homing migration of adult fish. Data on the molecular and genetic bases of olfactory chemoreception are presented. It is shown that the rates of homing (and straying) vary among species and among populations of the same species, depending on their biological and ecological features, on a variety of environmental factors and conditions, and anthropogenic impact. The negative effects of straying of farmed and hatchery salmon into natural populations are discussed.