, Volume 299, Issue 3, pp 179–183 | Cite as

Nocturnal emergence of juvenile rainbow trout from winter concealment relative to light intensity

  • Craig R. Contor
  • J. S. Griffith


This study examined the relationship between light intensity and the number of juvenile rainbow trout (Oncorhynchus mykiss) visible to a snorkeler during February in the Henrys Fork of the Snake River, Idaho, USA. Fish were concealed in the substratum during daylight. Emergence from concealment was observed from 30 to 80 min after real sunset time and began when stars were first visible (pyranometric irradiance, 4.5 × 10−3 W−2). Densities of visible fish were negatively correlated with light intensity (r2=0.81,P<0.001). Later at night, densities decreased in the presence of moonlight and artificial light. Fish were observed to feed at night.

Key words

rainbow trout Oncorhynchus mykiss winter stream ecology behaviour 


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Copyright information

© Kluwer Academic Publishers 1995

Authors and Affiliations

  • Craig R. Contor
    • 1
  • J. S. Griffith
    • 1
  1. 1.Department of Biological SciencesIdaho State UniversityPocatelloUSA

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