This thesis examined: 1) how ontogeny affects aspects of metabolic depression in the cunner; and 2) whether the stress response of adult cunner is modified during metabolic depression. The effect of decreasing temperature at 2°C per day on the metabolism of three size classes of ∼9°C acclimated cunner was studied. The onset-temperature for metabolic depression in cunner decreased with body size (age), i.e. 7°C in adult fish vs. 6°C and 5°C in small and young-of-the-year (YOY) fish, respectively. In contrast, the extent of metabolic depression was ∼80% (Q₁₀ = ∼15) for YOY fish, ∼65% (Q₁₀ = ∼8) for small fish, and ∼55% (Q₁₀ = ∼5) for adults. Stress hormone levels and steroidogenic transcript levels were measured in adult cunner acclimated at 0°C and 10°C. Fish at 10°C had 9.09 fold and 4.77 fold higher post-stress plasma epinephrine and norepinephrine levels, respectively, and 4.67 fold greater resting plasma cortisol levels (∼65 ng ml⁻¹) compared with 0°C fish (∼10 ng ml⁻¹). However, cortisol levels did not increase post-stress in 10°C fish, whereas 0°C fish had a 'typical' stress response with cortisol levels reaching ∼107 ng ml⁻¹ by 2 hours post-stress. Transcript levels of P450scc were 3.25 fold higher in the head kidney of 10°C fish compared with 0°C fish. However, there was no significant difference in StAR transcript levels in the head kidney of 10°C fish compared with 0°C fish. GR transcript levels were 1.70 fold and 1.29 fold lower in the head kidney and liver, respectively, of 10°C fish compared with 0°C fish
