Olfactory Imprinting and Homing in Salmon

Chance Favors Only the Prepared Mind How does a scientist go about the task of pushing back the curtains of the unknown? Certainly the romance of tackling the mysteries of nature provides the motivation, for who would not be inspired by the remarkable life history of this romantic beast, the salmon. After living in the Pacific Ocean for several years, salmon swim thousands of kilometers back to the stream of their birth to spawn. I have always been fascinated by the homing migration of salmon. Noone who has seen a 20-kilogram salmon fling itself into the air repeatedly until it is exhausted in a vain effort to surmount a waterfall can fail to marvel at the strength of the instinct that draws the salmon upriver to the stream where it was born. But how does it find its way back? I was puzzling over this problem during a family vacation in 1946. Inspired by the work of the great German Nobel Laureates, Karl von Frisch and Konrad Lorenz, I had been conducting research with my graduate student Theodore Walker, since 1945, on the ability of fishes to discriminate odors emanating from aquatic plants. Von Frisch had studied schooling minnows and discovered that, if broken, their skin emitted a con specific chemical substance, termed Schreckstoff, which caused other members of its school to disperse and hide.

Contenu

I Olfactory Imprinting and Homing in Salmon.- 1 Notes on the Life History of Coho Salmon.- 1.1 The Magic Journey: Migration of Salmon.- 1.2 Homing.- 1.3 Functions of Homing.- 1.4 Life History of Coho Salmon.- 1.4.1 Alevin Stage.- 1.4.2 Fry and Fingerling Stages.- 1.4.3 Transformation from Parr to Smolt.- 1.4.4 Ocean Life: Migration to the Spawning Site.- 1.5 Evidence for Imprinting: Transplantation Experiments.- 1.5.1 Transplantation Before or During the Smolt Stage.- 1.5.2 Transplantation After Smolt Transformation.- 1.5.3 Transportation of Smolts.- 1.5.4 Coincidence of Imprinting and Smolt Transformation.- 1.5.5 Stocking of Salmon in the Great Lakes.- 1.5.6 Summary of Transplantation Experiments.- 2 Imprinting to Olfactory Cues: The Basis for Home-Stream Selection by Salmon.- 2.1 Early Investigations of the Olfactory Hypothesis.- 2.1.1 Laboratory Conditioning Experiments.- 2.1.2 Sensory-Impairment Experiments.- 2.1.3 Experiments on Olfactory Recognition of the Home Stream: Effects of Attractants and Repellents.- 2.1.4 Electrophysiological Studies.- 2.1.5 Criticisms of Early Investigations.- 2.2 Experiments with Artificially Imprinted Salmon.- 2.2.1 Experiments in Southern Lake Michigan - Imprinting Salmon with Morpholine.- 2.2.2 Experiments in Northern Lake Michigan - Imprinting Salmon to Morpholine or Phenethyl Alcohol.- 2.2.3 Ultrasonic Tracking.- 2.2.4 Electroencephalography.- 2.2.5 Electrocardiography: Conditioning the Heart Rate of Salmon as an Indicator to Their Response to Synthetic Chemicals.- 2.3 Natural Imprinting.- 2.4 Mechanisms of Olfactory Orientation in Upstream Migration.- 2.4.1 Overshooting and Proving: Positive and Negative Rheotaxis.- 2.4.2 Rheotropic Responses of Salmon to Tidal Currents.- 2.4.3 Rheotropic Responses of Salmon Imprinted to Synthetic Chemicals.- 2.5 Pheromones and Homing.- II Hormonal Regulation of Smolt Transformation and Olfactory Imprinting in Salmon.- 3 Factors Influencing Smolt Transformation: Effects of Seasonal Fluctuations in Hormone Levels on Transitions in Morphology, Physiology, and Behavior.- 3.1 Morphological, Physiological, and Behavioral Transitions.- 3.1.1 Development of Silvery Coloration.- 3.1.2 Downstream Migratory Activity.- 3.1.3 Salinity Tolerance and Osmoregulation.- 3.1.4 Osmoregulatory Correctional Mechanisms in Smolts: Gill Na+ /K+-ATPase Activity.- 3.1.5 Fish with Freshwater Life Cycles.- 3.2 Comparative Aspects of Smolt Transformation.- 3.3 Evidence for Hormonal Regulation of Smolt Transformation.- 3.4 Hormonal Influences on Olfactory Sensitivity, Learning, and Memory in Salmonids.- 4 Fluctuations in Hormone Levels During the Spawning Migration: Effects on Olfactory Sensitivity to Imprinted Odors.- 4.1 Effect of Sex Hormones on Olfactory Sensitivity and Discrimination.- 4.2 Physiological Mechanism for Countering Olfactory Adaptation.- 5 Thyroid Activation of Olfactory Imprinting in Coho Salmon.- 5.1 Methods for Studying Hormonal Regulation of Smolt Transformation.- 5.1.1 Natural Smolts.- 5.1.2 Hormonally Induced Smolt Transformation.- 5.1.3 Quantification of Smolt Transitions.- 5.1.4 Silvering and Loss of Parr Marks.- 5.1.5 Downstream Migratory Behavior.- 5.1.6 Salinity Tolerance and Osmoregulatory Capability.- 5.1.7 Gill Na+/K+-ATPase Activity.- 5.1.8 Hormone Radioimmunoassay.- 5.2 Results of Experiments on Hormonal Regulation of Smolt Transformation.- 5.3 Experiments with Rainbow Trout.- 5.4 Methods for Studying Endocrine Control of Olfactory Imprinting.- 5.5 Results of Experiments on Endocrine Control of Olfactory Imprinting.- 5.5.1 Behavioral Tests.- 5.5.2 Electrophysiological Tests.- 5.6 Organizational Influence of Thyroid Hormones on Maturation of the Central Nervous System.- 6 Endogenous and Environmental Control of Smolt Transformation.- 6.1 Size.- 6.2 Water Temperature.- 6.3 Daylength.- 6.4 Endocrine Mediation of Photoperiodic Cues.- 6.4.1 Thyroid Hormones.- 6.4.2 Osmoregulatory Hormones.- 6.4.3 Time-Keeping Role of the Pineal Gland.- 6.5 Endogenous Factors Regulating Smolt Transformation.- 6.6 Influence of Daylength on the Smoltification Process and the Production of Thyroid Hormones.- Postscript.- References.