Metabolic enzyme activity during smolting in stream- and hatchery-reared Atlantic salmon (Salmo salar)

To evaluate the metabolic differences between Atlantic salmon (Salmo salar) parr and smolts and the effect of rearing environment, we examined metabolic enzyme activity in white muscle, liver, and heart in stream- and hatchery-reared juveniles. Spring increases in gill Na+,K+-ATPase (3.5-fold) and cardiosomatic index (37-69%) and decreases in condition factor (similar to 17%) occurred in smolts, but not in parr. White muscle phosphofructokinase (PFK) increased during spring and was 3.6-fold higher in smolts than in parr by late spring. There were seasonal increases in liver citrate synthase (CS) (similar to 42%), liver beta- hydroxyacyl-coenzyme A dehydrogenase (HOAD) (similar to 60%), and heart CS (similar to 23%) and decreases in liver lactate dehydrogenase (LDH) (similar to 28%) in parr and smolts. Activity of liver HOAD was greater in stream-reared smolts (similar to 18%) than in parr or hatchery smolts. Heart PFK activity increased during spring in wild-reared parr and smolts, while it decreased in hatchery-reared smolts. White muscle LDH and PFK increased earlier in spring in hatchery- than in stream-reared smolts. Our results suggest that increased heart size and high white muscle PFK occur during smolting and may be adaptive for downstream and ocean migration. Hatchery- and stream-reared Atlantic salmon differ in the timing of metabolic changes during smolting, which may impact their long-term survival.