Laboratory evaluation of phototaxis in cultured Cisco larvae

Abstract

Objective Field observations in a Lake Ontario embayment suggested that there is a phototaxic response of larval coregonines that changes with development. Methods We used a controlled laboratory experiment with hatchery-reared larvae exposed to three different light regimes (24-h light, 24-h dark, or 12-h light followed by 12-h dark) to test for phototaxis in Cisco Coregonus artedi . Results Larval depth distributions were not uniform, and contrasts between vertical distributions within early and late portions of the time series when larvae were exposed to light showed evidence of phototaxis and transition to a preference for the bottom around 68 d posthatch. Larval behavior in dark treatments contrasted with those exposed to light and also suggested that other influences on depth distribution could be operating. Conclusions As observed in other species, larval Cisco phototaxis response would likely result in diel vertical migrations and may be an adaptation to changes in food distributions balanced with predation risk as the larvae grow and become stronger swimmers. This has implications for the success of Cisco restoration in the Great Lakes, particularly as climate change affects environmental conditions and phenology.