Das Verhalten von Wanderaalen,Anguilla rostrata, gegenüber Strömung, Salzgehalt und Lunarperiode

Abstract

1. Behaviour of migratory silver eels and immature yellow eels,Anguilla rostrata, was studied in a choice-chamber apparatus. 2. Silver eels display a negative rheotaxis in both well water and natural stream water. 3. Silver eels reversed the sign of their response, to a positive rheotaxis, when salt water was introduced into the tank. 4. Rheotaxis and the salinity response are proposed as an effective orientation mechanism in the seaward migration of the silver eel. Responses are anticipatory in nature and are thought to be only part of a sequential arrangement of orientation behaviours. 5. Yellow eels showed no rheotactic response in August, but displayed a negative rheotaxis two months later into the fall. This seasonal difference in rheotactic responses of the yellow eels suggests periodic movement away from a home range in what might constitute a “dry run” for the eventual offshore migration. 6. Yellow and silver eels in heterogenous samples showed similar rheotactic responses in fresh water but were segregated by response in salt water. 7. The non-orientation of the yellow eels in the freshwater-saltwater choice suggests that it is the response to salinity which contains the yellow eel in its feeding habitat and later guides the silver eel away from it. 8. Perception of saltwater by silver eels is olfactory. 9. Locomotor activity of silver eels peaked to coincide with periods of naturally occurring darkness, between sunset and moonrise. The relationship between eel migration and lunar period is discussed in this respect. 10. Exogenous control over locomotor activity is indicated by experiments which induced activity during daylight hours. The presence of an endogenous factor is also suggested.