SEASONAL-VARIATION IN TEMPERATURE PREFERENCE OF JUVENILE ATLANTIC COD (GADUS-MORHUA), WITH EVIDENCE SUPPORTING AN ENERGETIC BASIS FOR THEIR DIEL VERTICAL MIGRATION

Juvenile (3-year-old) Atlantic cod (Gadus morhua) from Broad Cove, Conception Bay, Newfoundland, exhibit seasonal variation in temperature preference. Laboratory studies show that juvenile cod from ambient temperature water prefer temperatures that correlate closely with seasonal changes in the temperature of the inshore waters that they inhabit. A similar pattern is shown by fish held in 10-degrees-C water over winter, indicating that variation in temperature preference is not simply a response to changing ambient temperatures but occurs in an anticipatory manner that allows them to maintain their physiologically optimal temperature at a seasonally appropriate level. The results also support the hypothesis that the diel vertical migration of juvenile cod in summer increases energetic efficiency by reducing metabolic costs in nonfeeding hours.