Field observations in a Lake Ontario embayment suggested that there is a phototaxic response of larval cisco that changes with development. This switch was verified using cultured cisco in a laboratory environment. These data include counts of cisco larvae at three depth ranges within multiple 95 liter tanks. Each tank of larvae were exposed to one of three different light treatments with three replicate tanks per treatment. Light treatments were 24 hours per day of light exposure, 24 hours per day in darkness, and a 12-hour light then 12-hour dark exposure cycle. Observations of cisco positioning within the water column were recorded periodically. The information collected included the date and time of the observation, age of larvae at the time of the observation, and the count of larvae at each depth range at the time of the observation. Observations were recorded over 31 days.