Energy expenditure during hatching in rainbow trout (Oncorhynchus mykiss) embryos

The objective of our study was to estimate the overall (aerobic and anaerobic) energy expenditure involved in hatching in rainbow trout (Oncorhynchus mykiss) embryos. During hatching, there were significant increases (50% and 19%, respectively) in movement and oxygen consumption. There were no differences in tissue indicators of anaerobic metabolism (adenosine triphosphate (ATP), adenosine monophosphate (AMP) deaminase, ammonia) between embryos that hatched naturally (chorionated) compared with embryos in which the chorion had been manually removed and therefore did not hatch (dechorionated). Furthermore, phosphocreatine (PCr), ATP, and lactate were unaltered immediately after hatching compared with embryos at rest before hatch. The anaerobic capacity of just hatched larvae was further evaluated by forced exercise and hypoxic exposure. PCr and ATP were unaltered following a 2 min manual chase, whereas lactate concentration was significantly increased (30%). Hypoxia (5 mg (O2L-1)-L-., 5 days) resulted in a 2.7-fold elevation of tissue lactate concentration. Our results reveal that the increase in activity during hatch may be involved in escaping the egg capsule, but the metabolic cost of this increased movement is relatively small. Moreover, the anaerobic capacity of newly hatched rainbow trout is low relative to juvenile or adult fish.