Fish migration is important and spectacular. Migratory fish gather energy in one portion of the environment and transport it to other areas, where it often becomes available to humans or to other elements in the ecosystem. Migration brings fish into situations that allow easy harvest as they concentrate along migration routes. Their journeys also make them vulnerable to human intereference at critical points along their route. Salmon, for example, may harvest plankton in the open ocean and transport that food energy to coastal and inland regions, where it is captured by fisheries or deposited in inland streams and utilized by the flora and fauna of the region. These salmon are able to complete journeys of thousands of kilometers from their natal streams to oceanic feeding grounds and back to the same home streams, an accomplishment that strains our credi bili ty . We now understand some of the timing and guiding stimuli used in these migrations, and mechanisms can be logically proposed, on the basis of the established abilities of fishes, to account for the unexplained portions of the migrations. There is no single factor guiding these fish. Instead, they are dependent on the presence in their environment of a great variety of appropriate orienting and timing stimuli. These stimuli are vulnerable to human interference. The more widespread and easily available the information on these requirements, the more readily fish can be protected from such interference.

Table of Contents:
1. Introduction.- 2. Light.- 2.1 Light in Water.- 2.2 Fish Photoreceptors.- 2.2.1 Vision.- 2.2.1.1 Focusing.- 2.2.1.2 Adaptation to Brightness.- 2.2.1.3 Vision Through the Water Surface.- 2.2.1.4 Sensitivity to Polarized Light.- 2.2.1.5 Extraoptic Photoreceptors.- 2.3 Timing.- 2.3.1 Diel Timing.- 2.3.1.1 Detection of Diel Cycles of Illumination.- 2.3.1.2 The Priority of Migration Relative to Other Behaviour.- 2.3.1.3 Physiological Control of Diel Rhythms.- 2.3.1.4 Physiological Rhythms and Natural Migrations.- 2.3.1.5 Diurnal Timing of Salmon and Trout Migration.- 2.3.2 Seasonal Timing.- 2.3.2.1 Photoperiodic Control of Salinity Preference.- 2.3.2.2 Photoperiodic Timing of Smolt Migrations.- 2.3.2.3 Photoperiod and Sun-Compass Time Compensation.- 2.3.2.4 Photoperiodic Timing of Rheotaxis.- 2.3.2.5 Summary of Photoperiodic Timing.- 2.3.3 Lunar Timing.- 2.3.3.1 Lunar Timing of Activity Cycles Related to Tides.- 2.3.3.2 Moonlight.- 2.3.3.3 Summary of Lunar Timing.- 2.3.4 Social Interaction as a Visual Timing Mechanism.- 2.3.4.1 Social Facilitation as a Releasing Stimulus.- 2.3.4.2 Social Facilitation as a Priming Stimulus.- 2.3.4.3 Social Interaction and Dispersal.- 2.4 Direction and Distance.- 2.4.1 Landmarks.- 2.4.1.1 Pilotage by Familiar Landmarks...- 2.4.1.2 Use of Landmarks to Stay on Course.- 2.4.1.3 Use of General Landmarks as Indicators of Conditions.- 2.4.2 Celestial Orientation.- 2.4.2.1 Time Compensation in Celestial Orientation.- 2.4.2.2 Sun-Compass Orientation.- 2.4.2.3 Lunar and Stellar Orientation.- 2.4.2.4 Summary of Celestial Orientation.- 2.5 Summary.- 3. Chemical Information.- 3.1 Characteristics and Importance of Chemical Information in an Aqueous Environment.- 3.2 Fish Chemoreception.- 3.2.1 Olfaction.- 3.2.2 Gustation.- 3.2.3 Other Chemoreceptors.- 3.3 Timing by Chemical Stimuli.- 3.3.1 Diel Timing.- 3.3.2 Synchronization with Flood Conditions.- 3.3.3 Synchronization with Tidal Flow.- 3.3.4 Pheromones as Timing Cues.- 3.3.5 Emergency Responses.- 3.4 Direction and Distance.- 3.4.1 Oxygen and Carbon Dioxide.- 3.4.2 Salinity.- 3.4.2.1 Oceanic Migration of Salmon.- 3.4.2.2 Coastal Migration.- 3.4.2.3 Summary.- 3.4.3 Pollution.- 3.4.3.1 Gas Bubble Disease.- 3.4.3.2 Heavy Metals.- 3.4.3.3 Other Compounds.- 3.4.4 Distinctive Chemical Components of Natural Waters.- 3.4.4.1 Stream Selection by Elvers.- 3.4.4.2 Lakeward Movement by Sockeye Fry.- 3.4.4.3 Perception of Differences Between Lake Water and Creek Water.- 3.4.4.4 Chemical Stimuli in Homing.- 3.4.4.5 Home Stream Odour.- 3.4.4.6 Pheromones.- 3.4.4.7 Predator Odours.- 3.4.4.8 Food.- 3.5 Summary.- 4. Mechanical Stimuli.- 4.1 Mechanical Stimuli.- 4.2 Mechanoreceptors.- 4.2.1 Touch and Proprioception.- 4.2.2 Pressure.- 4.2.3 The Lateral Line System.- 4.2.4 Hearing.- 4.2.5 Gravity and Acceleration.- 4.3 Mechanoreception and Timing.- 4.3.1 Tidal Rhythms.- 4.3.2 Weather and Barometric Pressure Changes.- 4.3.3 Microseisms: Small Earthquakes.- 4.3.4 Changes in Water Level.- 4.4 Mechanical Direction and Distance.- 4.4.1 Water Currents.- 4.4.1.1 Water Velocity as a Limiting Factor.- 4.4.1.2 Transport by Water Currents...- 4.4.1.3 Rheotaxis.- 4.4.2 Human Modification of the Physical Environment.- 4.4.3 Hydrostatic Pressure.- 4.4.4 Sound.- 4.4.4.1 Sounds as Landmarks.- 4.4.4.2 Social Signals.- 4.4.4.3 Echolocation.- 4.4.4.4 Sound and the Directing of Fish Migrations.- 4.4.5 Inertial Guidance.- 4.5 Summary.- 5. Temperature.- 5.1 Introduction.- 5.2 Temperature Reception.- 5.3 Timing by Thermal Stimuli.- 5.3.1 Diel Timing by Thermal Stimuli.- 5.3.1.1 Migration and Daily Temperature Peaks.- 5.3.1.2 Temperature Preference and Diel Movements.- 5.3.1.3 Summary of Diel Timing by Temperature.- 5.3.2 Seasonal Timing by Thermal Stimuli.- 5.3.2.1 Diel Thermal Cycles and Seasonal Timing.- 5.3.2.2 Seasonal Temperature Trends as Timing Cues.- 5.4 Thermal Stimuli Controlling Direction and Distance.- 5.4.1 Temperature and Fish Distribution.- 5.4.2 Temperature Preference.- 5.4.2.1 The Measurement of Thermal Preference.- 5.4.2.2 Mechanisms for Selection of Preferred Temperature.- 5.4.3 Temperature as a Guidance Mechanism in Migration.- 5.4.3.1 Lakeward Orientation by Temperature.- 5.4.3.2 Onshore Migration.- 5.4.3.3 Summary of Thermal Guidance Mechanisms.- 5.4.4 Effects of Thermal Effluents.- 5.5 Summary.- 6. Electrical and Magnetic Stimuli.- 6.1 Electricity in Water.- 6.2 Electroreception.- 6.2.1 Passive Electroreception.- 6.2.2 Active Electroreception.- 6.2.3 Electrical Sensitivity in "Non-Electric" Fish.- 6.3 Electrical Timing.- 6.4 Electrical Stimuli Affecting Direction and Distance of Migration.- 6.4.1 Ocean Water Currents.- 6.4.2 Local Electric Fields.- 6.4.3 Bioelectric Effects.- 6.4.4 Active Electroreception.- 6.5 Magnetism.- 6.6 Magnetic Senses.- 6.6.1 The Leask Hypothesis of Magnetoreception.- 6.6.2 Magnetite-Based Magnetoreception.- 6.6.3 Magnetic Sensitivity in Non-Electric Fish.- 6.6.4 Magnetoreception in Fish with Specialized Electroreceptors.- 6.7 Magnetic Timing.- 6.8 Magnetic Stimuli and Direction and Distance.- 6.9 Summary.- 7. The Past: Learning and Genetics.- 7.1 Learning.- 7.2 Genetic Differences Between Fish Stocks.- 7.3 Genetic Control of Timing of Migration.- 7.4 Genetic Control of Migratory Direction.- 7.5 Summary.- 8. Conclusion.- References.- Systematic Index.