We examined total and tissue-specific energy content of upstream-migrating American shad (Alosa sapidissima) in the Connecticut River. Total energy depletion over the course of the 228-km migration ranged from 35 to 60%. The approximate contributions of different tissues to energy use during migration were white muscle 57%, subdermal fat 27%, red muscle 8%, viscera 6%, and liver 2%. American shad preferentially use energy stores in the skin and its subdermal fat layer (depleted by 63%) while sparing red muscle protein. Both lipid and protein were used as energy sources throughout migration, although lipids were depleted to a greater extent (e.g., white muscle lipid decreased 48% and protein 30%). Large fish expended 2-21% more energy during migration than small fish. Migrating to upriver sites (198-228 km) is 50-100% more energetically expensive than to lower river sections for females. This suggests that upriver range expansion may be limited by females in that they may have reached a threshold level of energy expenditure in this upriver area. American shad may possess physiological mechanisms for tissue-specific energy use allowing maintenance of critical tissues necessary for postspawning survival.

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Near-hatching embryonic little skates, Raja erinacea, are highly active within their egg capsules, displaying a characteristic tail beating, which pumps water through the capsule. We measured the metabolic rate of late-stage embryos to determine whether oxygen sufficient for the embryo's needs will diffuse through the egg capsule, and to assess the energetic cost of tail beating. Metabolic rate was inferred from oxygen consumption rates while embryos were in the capsules, unencapsulated, and anesthetized and unencapsulated. Anesthesia inhibited voluntary movements, including tail wagging, allowing an estimate of the standard metabolic rate (SMR). Averaged over five embryos, the SMR was 0.032 ± 0.004 ml O 2 g -1 hr -1 . There was no significant difference in metabolic rate between encapsulated (0.058 ± 0.009 ml O 2 g -1 hr -1 ) and unencapsulated (0.049 ± 0.009 ml O 2 g -1 hr -1 ) skates. Tail beating was found to be energetically expensive, requiring a 53%-81% increase over the SMR. From literature values for the oxygen permeability of the egg capsule we conclude that tail beating is required to supply sufficient oxygen to the embryonic skate. This observation is consistent with the proposal that actively pumping water through the capsule, by tail beating, has played an evolutionary role in the shape of the capsule.

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