CONDITION AND PERFORMANCE OF JUVENILE ATLANTIC SALMON (SALMO-SALAR) -EFFECTS OF REARING PRACTICES ON HATCHERY FISH AND COMPARISON WITH WILD FISH

This study examined the effects of various modifications of rearing pr actices on hatchery-reared Atlantic salmon (Salmo salar) fingerlings a nd compared condition and performance of hatchery fingerlings (age 0()) and yearlings (age 1(+)) with those of wild-reared Atlantic salmon. Reduced fish density land increased ration in rearing tanks promoted increased growth and condition factor and significant changes in muscl e composition, including increased muscle lipid content and glycolytic enzyme activity, specfically phosphofructokinase and lactate dehydrog enase. However, these changes had no effect on anaerobic capacity. Mor eover; swimming performance was poorer in fingerlings reared at low co mpared with normal density. Raising the water velocity from 0 to 4 cm . s(-1) (similar to 0.7 body length . s(-1)) had overall beneficial ef fects, most notably increased endurance in fixed velocity sprint tests and a reduction of ion loss in an epinephrine challenge test. Increas ing velocity to 9 cm . s(-1) had no further effects. Wild fingerlings were larger with better fin quality and superior anaerobic capacity an d swim performance. Even larger differences were seen between hatchery -reared and wild yearlings. It is concluded that significant changes i n morphology, physiology, and muscle biochemistry of juvenile Atlantic salmon can be brought about by changing hatchery rearing conditions, but these changes are of limited effectiveness in reducing the differe nce between hatchery-reared and wild fish.