Experimental Evidence for Olfactory Imprinting by Sockeye Salmon at Embryonic and Smolt Stages

Abstract

Anadromous salmonids have an extraordinary ability to migrate back to their natal streams to spawn as adults, but the mechanisms underlying this ability are not completely known. Many experiments indicate that salmon imprint on natal odors at the smolt stage prior to seaward migration, but the life history and population genetics of some species, notably Sockeye Salmon Oncorhynchus nerka, suggest that imprinting also occurs during the period between hatching and emergence from the gravel as fry. To test the hypothesis that Sockeye Salmon imprint during this period, we exposed juveniles to a mixture of odorants during either the alevin or smolt stage. The smolt exposure group was further divided into different exposure durations (6 weeks, 1 week, and 1 d) to evaluate the duration of odor exposure needed for imprinting during that stage. Imprinting was assessed by testing fish as mature adults in two-choice mazes containing unfamiliar water with and without the mixture of odorants. Fish exposed either as alevins or for 6 weeks as smolts both spent significantly more time in the odor-scented arm than control fish (unexposed to the odors as juveniles). Fish exposed to odors for 1 week or 1 d as smolts showed similar but weaker responses. Concurrent measures of gill Na + /K + -ATPase activity and plasma thyroxine confirmed that the fish exposed as smolts were undergoing parr-smolt transformation during exposure. We conclude that Sockeye Salmon imprinted as both alevins and smolts and that longer periods of odor exposure yielded greater behavioral responses to odors as adults, though specific times within the parr-smolt transformation period may be more sensitive to imprinting than others.

Differential Marking of Embryos by Location and Date of Release Reveals Within‐River Natal Homing and Parental Influence on Progeny Return Timing in Sockeye Salmon

“…Havey et al. () found that Sockeye Salmon imprinted to odors at both the alevin and smolt stages in laboratory conditions, and our work showed that fry released in the Cedar River imprinted at the initiation of downstream migration.…”

“…Experimental work has provided evidence of olfactory imprinting by fry (Havey et al. ), but the extent to which they express this ability in natural systems is unclear.…”

Steelhead Overshoot and Fallback Rates in the Columbia–Snake River Basin and the Influence of Hatchery and Hydrosystem Operations

“…Havey et al. () and Quinn et al. () found that imprinting begins during early rearing stages; therefore, constructing hatcheries upstream of release areas may result in unanticipated upstream movement by returning adults.…”

Sensory mechanisms of natal stream imprinting and homing in Oncorhynchus spp.

“…Also, the stimulation of guanylyl cyclase activity by PEA was significantly greater in olfactory cilia isolated from PEA-imprinted fish than in PEAnaïve fish at the time of the homing migration, which occurred 2 years after exposure to PEA (Dittman et al, 1997). Havey et al (2017) presented experimental evidence for olfactory imprinting to a mixture of odorants containing amino acids and PEA in O. nerka at the embryonic and smolt stages. However, there have been few attempts to identify the properties of natal-stream odours in salmonid populations of the eastern Pacific Ocean.…”

“…Havey et al . () presented experimental evidence for olfactory imprinting to a mixture of odorants containing amino acids and PEA in O. nerka at the embryonic and smolt stages. However, there have been few attempts to identify the properties of natal‐stream odours in salmonid populations of the eastern Pacific Ocean.…”