Growth and Lipid Composition of Winter Flounder Juveniles Reared under Natural and Fixed Photoperiod and Temperature Conditions

Abstract

AbstractIn age‐0 winter flounder Pseudopleuronectes americanus, a fixed long photoperiod (14.5 h light: 9.5 h dark) applied during the first 45 d postsettlement did not improve growth compared with fish held under natural photoperiod conditions. After being reared under these two regimes until 29 October, juveniles exposed to the long photoperiod after settlement were maintained under the same conditions during the winter, but temperature was not allowed to decrease below 4°C. Juveniles previously exposed to the natural photoperiod were maintained under one of the following conditions: (1) natural photoperiod and natural temperature (1–9°C), (2) natural photoperiod and a minimum winter temperature of 4°C, or (3) long photoperiod and a minimum temperature of 4°C. Most mortality (80%) occurred within the first 2 months of the experiment. Juveniles that experienced the transition from natural to long photoperiod conditions displayed higher growth through the winter than did juveniles exposed to natural conditions; at the end of winter, fish that were transitioned to the long photoperiod were 25% longer (19 mm), were twice as heavy (125 mg), and contained twice as much total lipids (803 μg/mg) and five times more triacylglycerols (24% of total lipids) than juveniles subjected to the natural photoperiod. These results indicate that we may be able to eliminate the winter fasting that occurs under natural conditions and to elicit winter growth in this species by using photoperiod manipulation. In addition, it appears that a decrease in photoperiod is needed for fish to respond to a subsequent increase in photoperiod.Received November 3, 2009; accepted May 27, 2010