Changes in phototaxis during early development of walleye

Phototaxis of walleyes Stizostedion vitreum vitreum was examined during the first 11 weeks of larva and juvenile development. Fish were subjected to six light intensities ranging from 2 to 34 lux, plus 7,800 lux as an extreme. The number of fish positioned in each light intensity was used to determine the phototactic response. Larvae and juveniles 1 to 8 weeks old (9 to 32 mm total length) were attracted to the highest light intensity (7,800 lux), and juveniles older than 8 weeks (32 to 40 mm long) aggregated at the lowest intensities (2 and 4 lux). The change from positive to negative phototaxis was more closely related to fish size than to age.